Add image placeholder and upload indicating frame (#1666)

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de> Co-authored-by: Philip Molares <philip.molares@udo.edu>
2024-11-21 17:26:29 -05:00 · 2021-12-11 15:34:33 +01:00 · 2021-12-11 15:34:33 +01:00 · d4251519e2
commit d4251519e2
parent 58fecc0b3a
37 changed files with 908 additions and 72 deletions
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@ -74,6 +74,8 @@ SPDX-License-Identifier: CC-BY-SA-4.0
 - The history page supports URL parameters that allow bookmarking of a specific search of tags filter.
 - Users can change the pinning state of a note directly from the editor.
 - Note information dialog containing word count, revision count, last editor and creation time.
+- Image tags with placeholder urls (`https://`) will be replaced with a placeholder frame.
+- Images that are currently uploading will be rendered as "uploading".

 ### Changed

--- a/cypress/integration/autocompletion.spec.ts
+++ b/cypress/integration/autocompletion.spec.ts
@ -16,16 +16,16 @@ describe('Autocompletion works for', () => {
      cy.get('.CodeMirror-hints').should('exist')
      cy.get('@codeinput').type('{enter}')
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-code > div:nth-of-type(1) > .CodeMirror-line > span > span').should('have.text', '```abnf')
-      cy.get('.CodeMirror-code > div:nth-of-type(3) > .CodeMirror-line > span > span').should('have.text', '```')
+      cy.get('.CodeMirror-code > div:nth-of-type(1) > .CodeMirror-line').contains('```abnf')
+      cy.get('.CodeMirror-code > div:nth-of-type(3) > .CodeMirror-line').contains('```')
      cy.getMarkdownBody().findById('highlighted-code-block').should('exist')
    })
    it('via doubleclick', () => {
      cy.setCodemirrorContent('```')
      cy.get('.CodeMirror-hints > li').first().dblclick()
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-code > div:nth-of-type(1) > .CodeMirror-line > span > span').should('have.text', '```abnf')
-      cy.get('.CodeMirror-code > div:nth-of-type(3) > .CodeMirror-line > span > span').should('have.text', '```')
+      cy.get('.CodeMirror-code > div:nth-of-type(1) > .CodeMirror-line').contains('```abnf')
+      cy.get('.CodeMirror-code > div:nth-of-type(3) > .CodeMirror-line').contains('```')
      cy.getMarkdownBody().findById('highlighted-code-block').should('exist')
    })
  })
@ -36,17 +36,17 @@ describe('Autocompletion works for', () => {
      cy.get('.CodeMirror-hints').should('exist')
      cy.get('@codeinput').type('{enter}')
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-code > div:nth-of-type(1) > .CodeMirror-line > span > span').should('have.text', ':::success')
-      cy.get('.CodeMirror-code > div:nth-of-type(3) > .CodeMirror-line > span > span').should('have.text', '::: ')
-      cy.getMarkdownBody().find('div.alert').should('exist')
+      cy.get('.CodeMirror-code > div:nth-of-type(1) > .CodeMirror-line').contains(':::success')
+      cy.get('.CodeMirror-code > div:nth-of-type(3) > .CodeMirror-line').contains('::: ')
+      cy.getMarkdownBody().find('.alert').should('exist')
    })
    it('via doubleclick', () => {
      cy.setCodemirrorContent(':::')
      cy.get('.CodeMirror-hints > li').first().dblclick()
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-code > div:nth-of-type(1) > .CodeMirror-line > span > span').should('have.text', ':::success')
-      cy.get('.CodeMirror-code > div:nth-of-type(3) > .CodeMirror-line > span > span').should('have.text', '::: ')
-      cy.getMarkdownBody().find('div.alert').should('exist')
+      cy.get('.CodeMirror-code > div:nth-of-type(1) > .CodeMirror-line').contains(':::success')
+      cy.get('.CodeMirror-code > div:nth-of-type(3) > .CodeMirror-line').contains('::: ')
+      cy.getMarkdownBody().find('.alert').should('exist')
    })
  })

@ -57,13 +57,13 @@ describe('Autocompletion works for', () => {
        cy.get('.CodeMirror-hints').should('exist')
        cy.get('@codeinput').type('{enter}')
        cy.get('.CodeMirror-hints').should('not.exist')
-        cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', ':hedgehog:')
+        cy.get('.CodeMirror-activeline').contains(':hedgehog:')
      })
      it('via doubleclick', () => {
        cy.setCodemirrorContent(':hedg')
        cy.get('.CodeMirror-hints > li').first().dblclick()
        cy.get('.CodeMirror-hints').should('not.exist')
-        cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', ':hedgehog:')
+        cy.get('.CodeMirror-activeline').contains(':hedgehog:')
      })
    })

@ -73,13 +73,13 @@ describe('Autocompletion works for', () => {
        cy.get('.CodeMirror-hints').should('exist')
        cy.get('@codeinput').type('{enter}')
        cy.get('.CodeMirror-hints').should('not.exist')
-        cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', ':fa-facebook:')
+        cy.get('.CodeMirror-activeline').contains(':fa-facebook:')
      })
      it('via doubleclick', () => {
        cy.setCodemirrorContent(':fa-face')
        cy.get('.CodeMirror-hints > li').first().dblclick()
        cy.get('.CodeMirror-hints').should('not.exist')
-        cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', ':fa-facebook:')
+        cy.get('.CodeMirror-activeline').contains(':fa-facebook:')
      })
    })
  })
@ -90,14 +90,14 @@ describe('Autocompletion works for', () => {
      cy.get('.CodeMirror-hints').should('exist')
      cy.get('@codeinput').type('{enter}')
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '# ')
+      cy.get('.CodeMirror-activeline').contains('# ')
      cy.getMarkdownBody().find('h1').should('have.text', '\n ')
    })
    it('via doubleclick', () => {
      cy.setCodemirrorContent('#')
      cy.get('.CodeMirror-hints > li').first().dblclick()
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '# ')
+      cy.get('.CodeMirror-activeline').contains('# ')
      cy.getMarkdownBody().find('h1').should('have.text', '\n ')
    })
  })
@ -108,23 +108,15 @@ describe('Autocompletion works for', () => {
      cy.get('.CodeMirror-hints').should('exist')
      cy.get('@codeinput').type('{enter}')
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '![image alt](https:// "title")')
-      cy.getMarkdownBody()
-        .find('p > img')
-        .should('have.attr', 'alt', 'image alt')
-        .should('have.attr', 'src', 'https://')
-        .should('have.attr', 'title', 'title')
+      cy.get('.CodeMirror-activeline').contains('![image alt](https:// "title")')
+      cy.getMarkdownBody().find('.image-drop').should('exist')
    })
    it('via doubleclick', () => {
      cy.setCodemirrorContent('!')
      cy.get('.CodeMirror-hints > li').first().dblclick()
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '![image alt](https:// "title")')
-      cy.getMarkdownBody()
-        .find('p > img')
-        .should('have.attr', 'alt', 'image alt')
-        .should('have.attr', 'src', 'https://')
-        .should('have.attr', 'title', 'title')
+      cy.get('.CodeMirror-activeline').contains('![image alt](https:// "title")')
+      cy.getMarkdownBody().find('.image-drop').should('exist')
    })
  })

@ -134,7 +126,7 @@ describe('Autocompletion works for', () => {
      cy.get('.CodeMirror-hints').should('exist')
      cy.get('@codeinput').type('{enter}')
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '[link text](https:// "title") ')
+      cy.get('.CodeMirror-activeline').contains('[link text](https:// "title") ')
      cy.getMarkdownBody()
        .find('p > a')
        .should('have.text', 'link text')
@ -145,7 +137,7 @@ describe('Autocompletion works for', () => {
      cy.setCodemirrorContent('[')
      cy.get('.CodeMirror-hints > li').first().dblclick()
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '[link text](https:// "title") ')
+      cy.get('.CodeMirror-activeline').contains('[link text](https:// "title") ')
      cy.getMarkdownBody()
        .find('p > a')
        .should('have.text', 'link text')
@ -160,14 +152,14 @@ describe('Autocompletion works for', () => {
      cy.get('.CodeMirror-hints').should('exist')
      cy.get('@codeinput').type('{enter}')
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '{%pdf https:// %}')
+      cy.get('.CodeMirror-activeline').contains('{%pdf https:// %}')
      cy.getMarkdownBody().find('p').should('exist')
    })
    it('via doubleclick', () => {
      cy.setCodemirrorContent('{')
      cy.get('.CodeMirror-hints > li').first().dblclick()
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '{%pdf https:// %}')
+      cy.get('.CodeMirror-activeline').contains('{%pdf https:// %}')
      cy.getMarkdownBody().find('p').should('exist')
    })
  })
@ -178,14 +170,14 @@ describe('Autocompletion works for', () => {
      cy.get('.CodeMirror-hints').should('exist')
      cy.get('@codeinput').type('{enter}')
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '</details>') // after selecting the hint, the last line of the inserted suggestion is active
+      cy.get('.CodeMirror-activeline').contains('</details>') // after selecting the hint, the last line of the inserted suggestion is active
      cy.getMarkdownBody().find('details').should('exist')
    })
    it('via doubleclick', () => {
      cy.setCodemirrorContent('<d')
      cy.get('.CodeMirror-hints > li').first().dblclick()
      cy.get('.CodeMirror-hints').should('not.exist')
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', '</details>')
+      cy.get('.CodeMirror-activeline').contains('</details>')
      cy.getMarkdownBody().find('details').should('exist')
    })
  })
--- a/cypress/integration/fileUpload.spec.ts
+++ b/cypress/integration/fileUpload.spec.ts
@ -42,7 +42,7 @@ describe('File upload', () => {
    it('via button', () => {
      cy.getById('editor-toolbar-upload-image-button').click()
      cy.getById('editor-toolbar-upload-image-input').attachFile({ filePath: 'demo.png', mimeType: 'image/png' })
-      cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', `![](${imageUrl})`)
+      cy.get('.CodeMirror-activeline').contains(`![](${imageUrl})`)
    })

    it('via paste', () => {
@ -54,7 +54,7 @@ describe('File upload', () => {
          }
        }
        cy.get('.CodeMirror-scroll').trigger('paste', pasteEvent)
-        cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', `![](${imageUrl})`)
+        cy.get('.CodeMirror-activeline').contains(`![](${imageUrl})`)
      })
    })

@ -68,7 +68,7 @@ describe('File upload', () => {
        }
        cy.get('.CodeMirror-scroll').trigger('dragenter', dropEvent)
        cy.get('.CodeMirror-scroll').trigger('drop', dropEvent)
-        cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', `![](${imageUrl})`)
+        cy.get('.CodeMirror-activeline').contains(`![](${imageUrl})`)
      })
    })
  })
@ -87,7 +87,7 @@ describe('File upload', () => {
    cy.fixture('demo.png').then(() => {
      cy.getById('editor-toolbar-upload-image-input').attachFile({ filePath: 'demo.png', mimeType: 'image/png' })
    })
-    cy.get('.CodeMirror-activeline > .CodeMirror-line > span > span').should('have.text', String.fromCharCode(8203)) //thanks codemirror....
+    cy.get('.CodeMirror-activeline').contains('![upload of demo.png failed]()')
  })

  it('lets text paste still work', () => {
@ -98,6 +98,6 @@ describe('File upload', () => {
      }
    }
    cy.get('.CodeMirror-scroll').trigger('paste', pasteEvent)
-    cy.get('.CodeMirror-activeline > .CodeMirror-line > span').should('have.text', `${testText}`)
+    cy.get('.CodeMirror-activeline').contains(`${testText}`)
  })
 })
--- a/locales/en.json
+++ b/locales/en.json
@ -34,6 +34,9 @@
        },
        "clickShield": {
          "previewHoverText": "Click to load content from {{target}}"
+        },
+        "uploadIndicator": {
+          "uploadMessage": "Uploading file"
        }
    },
    "landing": {
@ -202,8 +205,12 @@
    },
    "editor": {
        "upload": {
-            "uploadFile": "Uploading file...{{fileName}}",
-            "dropImage": "Drop Image to insert"
+            "uploadFile": {
+              "withoutDescription": "Uploading file {{fileName}}",
+              "withDescription": "Uploading file {{fileName}} - {{description}}"
+            },
+            "dropImage": "Drop Image to insert",
+            "failed": "Error while uploading {{fileName}}"
        },
        "untitledNote": "Untitled",
        "placeholder": "← Start by entering a title here\n===\nVisit the features page if you don't know what to do.\nHappy hacking :)",
@ -451,7 +458,11 @@
            }
        },
        "embeddings": {
-            "clickToLoad": "Click to load"
+            "clickToLoad": "Click to load",
+            "placeholderImage": {
+                "placeholderText": "Placeholder",
+                "upload": "Upload image"
+            }
        }
    },
    "views": {
--- a/src/api/media/index.ts
+++ b/src/api/media/index.ts
@ -4,7 +4,7 @@
 * SPDX-License-Identifier: AGPL-3.0-only
 */

-import { isMockMode } from '../../utils/test-modes'
+import { isMockMode, isTestMode } from '../../utils/test-modes'
 import { defaultFetchConfig, expectResponseCode, getApiUrl } from '../utils'

 export interface ImageProxyResponse {
@ -37,6 +37,13 @@ export const uploadFile = async (noteId: string, media: Blob): Promise<UploadedM
    method: isMockMode() ? 'GET' : 'POST',
    body: isMockMode() ? undefined : media
  })
+
+  if (isMockMode() && !isTestMode()) {
+    await new Promise((resolve) => {
+      setTimeout(resolve, 3000)
+    })
+  }
+
  expectResponseCode(response, isMockMode() ? 200 : 201)
  return (await response.json()) as Promise<UploadedMedia>
 }
--- a/src/components/common/upload-image-mimetypes.ts
+++ b/src/components/common/upload-image-mimetypes.ts
@ -18,3 +18,5 @@ export const supportedMimeTypes: string[] = [
  'image/tiff',
  'image/webp'
 ]
+
+export const acceptedMimeTypes = supportedMimeTypes.join(', ')
--- a/src/components/editor-page/editor-pane/editor-pane.tsx
+++ b/src/components/editor-page/editor-pane/editor-pane.tsx
@ -23,10 +23,11 @@ import { useOnEditorScroll } from './hooks/use-on-editor-scroll'
 import { useApplyScrollState } from './hooks/use-apply-scroll-state'
 import { MaxLengthWarning } from './max-length-warning/max-length-warning'
 import { useCreateStatusBarInfo } from './hooks/use-create-status-bar-info'
+import { useOnImageUploadFromRenderer } from './hooks/use-on-image-upload-from-renderer'

 const onChange = (editor: Editor) => {
+  const searchTerm = findWordAtCursor(editor)
  for (const hinter of allHinters) {
-    const searchTerm = findWordAtCursor(editor)
    if (hinter.wordRegExp.test(searchTerm.text)) {
      editor.showHint({
        hint: hinter.hint,
@ -55,6 +56,8 @@ export const EditorPane: React.FC<ScrollProps> = ({ scrollState, onScroll, onMak

  const [statusBarInfo, updateStatusBarInfo] = useCreateStatusBarInfo()

+  useOnImageUploadFromRenderer(editor)
+
  const onEditorDidMount = useCallback(
    (mountedEditor: Editor) => {
      updateStatusBarInfo(mountedEditor)
--- a/src/components/editor-page/editor-pane/find-regex-match-in-text.test.ts
+++ b/src/components/editor-page/editor-pane/find-regex-match-in-text.test.ts
@ -0,0 +1,38 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { findRegexMatchInText } from './find-regex-match-in-text'
+
+describe('find regex index in line', function () {
+  it('finds the first occurrence', () => {
+    const result = findRegexMatchInText('aba', /a/g, 0)
+    expect(result).toBeDefined()
+    expect(result).toHaveLength(1)
+    expect((result as RegExpMatchArray).index).toBe(0)
+  })
+
+  it('finds another occurrence', () => {
+    const result = findRegexMatchInText('aba', /a/g, 1)
+    expect(result).toBeDefined()
+    expect(result).toHaveLength(1)
+    expect((result as RegExpMatchArray).index).toBe(2)
+  })
+
+  it('fails to find with a wrong regex', () => {
+    const result = findRegexMatchInText('aba', /c/g, 0)
+    expect(result).not.toBeDefined()
+  })
+
+  it('fails to find with a negative wanted index', () => {
+    const result = findRegexMatchInText('aba', /a/g, -1)
+    expect(result).not.toBeDefined()
+  })
+
+  it('fails to find if the index is to high', () => {
+    const result = findRegexMatchInText('aba', /a/g, 100)
+    expect(result).not.toBeDefined()
+  })
+})
--- a/src/components/editor-page/editor-pane/find-regex-match-in-text.ts
+++ b/src/components/editor-page/editor-pane/find-regex-match-in-text.ts
@ -0,0 +1,26 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+/**
+ * Matches a regex against a given text and returns the n-th match of the regex.
+ *
+ * @param text The text that should be searched through
+ * @param regex The regex that should find matches in the text
+ * @param matchIndex The index of the match to find
+ * @return The regex match of the found occurrence or undefined if no match could be found
+ */
+export const findRegexMatchInText = (text: string, regex: RegExp, matchIndex: number): RegExpMatchArray | undefined => {
+  if (matchIndex < 0) {
+    return
+  }
+  let currentIndex = 0
+  for (const match of text.matchAll(regex)) {
+    if (currentIndex === matchIndex) {
+      return match
+    }
+    currentIndex += 1
+  }
+}
--- a/src/components/editor-page/editor-pane/hooks/use-on-image-upload-from-renderer.ts
+++ b/src/components/editor-page/editor-pane/hooks/use-on-image-upload-from-renderer.ts
@ -0,0 +1,120 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { useEditorReceiveHandler } from '../../../render-page/window-post-message-communicator/hooks/use-editor-receive-handler'
+import type { ImageUploadMessage } from '../../../render-page/window-post-message-communicator/rendering-message'
+import { CommunicationMessageType } from '../../../render-page/window-post-message-communicator/rendering-message'
+import { useCallback } from 'react'
+import { store } from '../../../../redux'
+import { handleUpload } from '../upload-handler'
+import type { Editor, Position } from 'codemirror'
+import { Logger } from '../../../../utils/logger'
+import { findRegexMatchInText } from '../find-regex-match-in-text'
+import Optional from 'optional-js'
+
+const log = new Logger('useOnImageUpload')
+const imageWithPlaceholderLinkRegex = /!\[([^\]]*)]\(https:\/\/([^)]*)\)/g
+
+/**
+ * Receives {@link CommunicationMessageType.IMAGE_UPLOAD image upload events} via iframe communication and processes the attached uploads.
+ *
+ * @param editor The {@link Editor codemirror editor} that should be used to change the markdown code
+ */
+export const useOnImageUploadFromRenderer = (editor: Editor | undefined): void => {
+  useEditorReceiveHandler(
+    CommunicationMessageType.IMAGE_UPLOAD,
+    useCallback(
+      (values: ImageUploadMessage) => {
+        const { dataUri, fileName, lineIndex, placeholderIndexInLine } = values
+        if (!editor) {
+          return
+        }
+        if (!dataUri.startsWith('data:image/')) {
+          log.error('Received uri is no data uri and image!')
+          return
+        }
+
+        fetch(dataUri)
+          .then((result) => result.blob())
+          .then((blob) => {
+            const file = new File([blob], fileName, { type: blob.type })
+            const { cursorFrom, cursorTo, description, additionalText } = Optional.ofNullable(lineIndex)
+              .map((actualLineIndex) => findPlaceholderInMarkdownContent(actualLineIndex, placeholderIndexInLine))
+              .orElseGet(() => calculateInsertAtCurrentCursorPosition(editor))
+            handleUpload(file, editor, cursorFrom, cursorTo, description, additionalText)
+          })
+          .catch((error) => log.error(error))
+      },
+      [editor]
+    )
+  )
+}
+
+export interface ExtractResult {
+  cursorFrom: Position
+  cursorTo: Position
+  description?: string
+  additionalText?: string
+}
+
+/**
+ * Calculates the start and end cursor position of the right image placeholder in the current markdown content.
+ *
+ * @param lineIndex The index of the line to change in the current markdown content.
+ * @param replacementIndexInLine If multiple image placeholders are present in the target line then this number describes the index of the wanted placeholder.
+ * @return the calculated start and end position or undefined if no position could be determined
+ */
+const findPlaceholderInMarkdownContent = (lineIndex: number, replacementIndexInLine = 0): ExtractResult | undefined => {
+  const currentMarkdownContentLines = store.getState().noteDetails.markdownContent.split('\n')
+  const lineAtIndex = currentMarkdownContentLines[lineIndex]
+  if (lineAtIndex === undefined) {
+    return
+  }
+  return findImagePlaceholderInLine(currentMarkdownContentLines[lineIndex], lineIndex, replacementIndexInLine)
+}
+
+/**
+ * Tries to find the right image placeholder in the given line.
+ *
+ * @param line The line that should be inspected
+ * @param lineIndex The index of the line in the document
+ * @param replacementIndexInLine If multiple image placeholders are present in the target line then this number describes the index of the wanted placeholder.
+ * @return the calculated start and end position or undefined if no position could be determined
+ */
+const findImagePlaceholderInLine = (
+  line: string,
+  lineIndex: number,
+  replacementIndexInLine = 0
+): ExtractResult | undefined => {
+  const startOfImageTag = findRegexMatchInText(line, imageWithPlaceholderLinkRegex, replacementIndexInLine)
+  if (startOfImageTag === undefined || startOfImageTag.index === undefined) {
+    return
+  }
+
+  return {
+    cursorFrom: {
+      ch: startOfImageTag.index,
+      line: lineIndex
+    },
+    cursorTo: {
+      ch: startOfImageTag.index + startOfImageTag[0].length,
+      line: lineIndex
+    },
+    description: startOfImageTag[1],
+    additionalText: startOfImageTag[2]
+  }
+}
+
+/**
+ * Calculates a fallback position that is the current editor cursor position.
+ * This wouldn't replace anything and only insert.
+ *
+ * @param editor The editor whose cursor should be used
+ */
+const calculateInsertAtCurrentCursorPosition = (editor: Editor): ExtractResult => {
+  const editorCursor = editor.getCursor()
+  return { cursorFrom: editorCursor, cursorTo: editorCursor }
+}
--- a/src/components/editor-page/editor-pane/tool-bar/upload-image-button.tsx
+++ b/src/components/editor-page/editor-pane/tool-bar/upload-image-button.tsx
@ -11,15 +11,13 @@ import { useTranslation } from 'react-i18next'
 import { ForkAwesomeIcon } from '../../../common/fork-awesome/fork-awesome-icon'
 import { UploadInput } from '../../sidebar/upload-input'
 import { handleUpload } from '../upload-handler'
-import { supportedMimeTypes } from '../../../common/upload-image-mimetypes'
+import { acceptedMimeTypes } from '../../../common/upload-image-mimetypes'
 import { cypressId } from '../../../../utils/cypress-attribute'

 export interface UploadImageButtonProps {
  editor?: Editor
 }

-const acceptedMimeTypes = supportedMimeTypes.join(', ')
-
 export const UploadImageButton: React.FC<UploadImageButtonProps> = ({ editor }) => {
  const { t } = useTranslation()
  const clickRef = useRef<() => void>()
--- a/src/components/editor-page/editor-pane/upload-handler.ts
+++ b/src/components/editor-page/editor-pane/upload-handler.ts
@ -4,36 +4,57 @@
 * SPDX-License-Identifier: AGPL-3.0-only
 */

-import type { Editor } from 'codemirror'
-import { t } from 'i18next'
+import type { Editor, Position } from 'codemirror'
 import { uploadFile } from '../../../api/media'
 import { store } from '../../../redux'
 import { supportedMimeTypes } from '../../common/upload-image-mimetypes'
-import { Logger } from '../../../utils/logger'
+import { replaceInMarkdownContent } from '../../../redux/note-details/methods'
+import { t } from 'i18next'
+import { showErrorNotification } from '../../../redux/ui-notifications/methods'

-const log = new Logger('File Uploader Handler')
-
-export const handleUpload = (file: File, editor: Editor): void => {
+/**
+ * Uploads the given file and writes the progress into the given editor at the given cursor positions.
+ *
+ * @param file The file to upload
+ * @param editor The editor that should be used to show the progress
+ * @param cursorFrom The position where the progress message should be placed
+ * @param cursorTo An optional position that should be used to replace content in the editor
+ * @param imageDescription The text that should be used in the description part of the resulting image tag
+ * @param additionalUrlText Additional text that should be inserted behind the link but within the tag
+ */
+export const handleUpload = (
+  file: File,
+  editor: Editor,
+  cursorFrom?: Position,
+  cursorTo?: Position,
+  imageDescription?: string,
+  additionalUrlText?: string
+): void => {
  if (!file) {
    return
  }
  if (!supportedMimeTypes.includes(file.type)) {
-    // this mimetype is not supported
    return
  }
-  const cursor = editor.getCursor()
-  const uploadPlaceholder = `![${t('editor.upload.uploadFile', { fileName: file.name })}]()`
+  const randomId = Math.random().toString(36).slice(7)
+  const uploadFileInfo =
+    imageDescription !== undefined
+      ? t('editor.upload.uploadFile.withDescription', { fileName: file.name, description: imageDescription })
+      : t('editor.upload.uploadFile.withoutDescription', { fileName: file.name })
+
+  const uploadPlaceholder = `![${uploadFileInfo}](upload-${randomId}${additionalUrlText ?? ''})`
  const noteId = store.getState().noteDetails.id
  const insertCode = (replacement: string) => {
-    editor.replaceRange(replacement, cursor, { line: cursor.line, ch: cursor.ch + uploadPlaceholder.length }, '+input')
+    replaceInMarkdownContent(uploadPlaceholder, replacement)
  }
-  editor.replaceRange(uploadPlaceholder, cursor, cursor, '+input')
+
+  editor.replaceRange(uploadPlaceholder, cursorFrom ?? editor.getCursor(), cursorTo, '+input')
  uploadFile(noteId, file)
    .then(({ link }) => {
-      insertCode(`![](${link})`)
+      insertCode(`![${imageDescription ?? ''}](${link}${additionalUrlText ?? ''})`)
    })
    .catch((error: Error) => {
-      log.error('error while uploading file', error)
-      insertCode('')
+      showErrorNotification('editor.upload.failed', { fileName: file.name })(error)
+      insertCode(`![upload of ${file.name} failed]()`)
    })
 }
--- a/src/components/markdown-renderer/document-markdown-renderer.tsx
+++ b/src/components/markdown-renderer/document-markdown-renderer.tsx
@ -46,7 +46,7 @@ export const DocumentMarkdownRenderer: React.FC<DocumentMarkdownRendererProps> =
    baseUrl,
    currentLineMarkers,
    useMemo(() => [new HeadlineAnchorsMarkdownExtension()], []),
-    lineOffset,
+    lineOffset ?? 0,
    onTaskCheckedChange,
    onImageClick,
    onTocChange
--- a/src/components/markdown-renderer/hooks/use-convert-markdown-to-react-dom.ts
+++ b/src/components/markdown-renderer/hooks/use-convert-markdown-to-react-dom.ts
@ -78,6 +78,8 @@ export const useConvertMarkdownToReactDom = (
  return useMemo(() => {
    const html = markdownIt.render(markdownCode)

+    htmlToReactTransformer.resetReplacers()
+
    return convertHtmlToReact(html, {
      transform: (node, index) => htmlToReactTransformer.translateNodeToReactElement(node, index),
      preprocessNodes: (document) => nodePreProcessor(document)
--- a/src/components/markdown-renderer/hooks/use-markdown-extensions.ts
+++ b/src/components/markdown-renderer/hooks/use-markdown-extensions.ts
@ -40,6 +40,8 @@ import type { ImageClickHandler } from '../markdown-extension/image/proxy-image-
 import type { TocAst } from 'markdown-it-toc-done-right'
 import type { MarkdownExtension } from '../markdown-extension/markdown-extension'
 import { IframeCapsuleMarkdownExtension } from '../markdown-extension/iframe-capsule/iframe-capsule-markdown-extension'
+import { ImagePlaceholderMarkdownExtension } from '../markdown-extension/image-placeholder/image-placeholder-markdown-extension'
+import { UploadIndicatingImageFrameMarkdownExtension } from '../markdown-extension/upload-indicating-image-frame/upload-indicating-image-frame-markdown-extension'

 /**
 * Provides a list of {@link MarkdownExtension markdown extensions} that is a combination of the common extensions and the given additional.
@ -57,7 +59,7 @@ export const useMarkdownExtensions = (
  baseUrl: string,
  currentLineMarkers: MutableRefObject<LineMarkers[] | undefined> | undefined,
  additionalExtensions: MarkdownExtension[],
-  lineOffset?: number,
+  lineOffset: number,
  onTaskCheckedChange?: (lineInMarkdown: number, checked: boolean) => void,
  onImageClick?: ImageClickHandler,
  onTocChange?: (ast?: TocAst) => void
@ -71,10 +73,12 @@ export const useMarkdownExtensions = (
      new VegaLiteMarkdownExtension(),
      new MarkmapMarkdownExtension(),
      new LinemarkerMarkdownExtension(
-        currentLineMarkers ? (lineMarkers) => (currentLineMarkers.current = lineMarkers) : undefined,
-        lineOffset
+        lineOffset,
+        currentLineMarkers ? (lineMarkers) => (currentLineMarkers.current = lineMarkers) : undefined
      ),
      new IframeCapsuleMarkdownExtension(),
+      new ImagePlaceholderMarkdownExtension(lineOffset),
+      new UploadIndicatingImageFrameMarkdownExtension(),
      new GistMarkdownExtension(),
      new YoutubeMarkdownExtension(),
      new VimeoMarkdownExtension(),
--- a/src/components/markdown-renderer/markdown-extension/image-placeholder/add-line-to-placeholder-image-tags.ts
+++ b/src/components/markdown-renderer/markdown-extension/image-placeholder/add-line-to-placeholder-image-tags.ts
@ -0,0 +1,35 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type MarkdownIt from 'markdown-it/lib'
+import { ImagePlaceholderMarkdownExtension } from './image-placeholder-markdown-extension'
+
+/**
+ * A {@link MarkdownIt.PluginSimple markdown it plugin} that adds the line number of the markdown code to every placeholder image.
+ *
+ * @param markdownIt The markdown it instance to which the plugin should be added
+ */
+export const addLineToPlaceholderImageTags: MarkdownIt.PluginSimple = (markdownIt: MarkdownIt) => {
+  markdownIt.core.ruler.push('image-placeholder', (state) => {
+    state.tokens.forEach((token) => {
+      if (token.type !== 'inline') {
+        return
+      }
+      token.children?.forEach((childToken) => {
+        if (
+          childToken.type === 'image' &&
+          childToken.attrGet('src') === ImagePlaceholderMarkdownExtension.PLACEHOLDER_URL
+        ) {
+          const line = token.map?.[0]
+          if (line !== undefined) {
+            childToken.attrSet('data-line', String(line))
+          }
+        }
+      })
+    })
+    return true
+  })
+}
--- a/src/components/markdown-renderer/markdown-extension/image-placeholder/hooks/use-on-image-upload.ts
+++ b/src/components/markdown-renderer/markdown-extension/image-placeholder/hooks/use-on-image-upload.ts
@ -0,0 +1,57 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { useRendererToEditorCommunicator } from '../../../../editor-page/render-context/renderer-to-editor-communicator-context-provider'
+import { useCallback } from 'react'
+import { CommunicationMessageType } from '../../../../render-page/window-post-message-communicator/rendering-message'
+import { Logger } from '../../../../../utils/logger'
+
+const log = new Logger('useOnImageUpload')
+
+/**
+ * Converts a {@link File} to a data url.
+ *
+ * @param file The file to convert
+ * @return The file content represented as data url
+ */
+const readFileAsDataUrl = (file: File): Promise<string> => {
+  return new Promise((resolve, reject) => {
+    const reader = new FileReader()
+    reader.readAsDataURL(file)
+    reader.onload = () => resolve(reader.result as string)
+    reader.onerror = (error) => reject(error)
+  })
+}
+
+/**
+ * Provides a callback that sends a {@link File file} to the editor via iframe communication.
+ *
+ * @param lineIndex The index of the line in the markdown content where the placeholder is defined
+ * @param placeholderIndexInLine The index of the placeholder in the markdown content line
+ */
+export const useOnImageUpload = (
+  lineIndex: number | undefined,
+  placeholderIndexInLine: number | undefined
+): ((file: File) => void) => {
+  const communicator = useRendererToEditorCommunicator()
+
+  return useCallback(
+    (file: File) => {
+      readFileAsDataUrl(file)
+        .then((dataUri) => {
+          communicator.sendMessageToOtherSide({
+            type: CommunicationMessageType.IMAGE_UPLOAD,
+            dataUri,
+            fileName: file.name,
+            lineIndex,
+            placeholderIndexInLine
+          })
+        })
+        .catch((error: ProgressEvent) => log.error('Error while uploading image', error))
+    },
+    [communicator, placeholderIndexInLine, lineIndex]
+  )
+}
--- a/src/components/markdown-renderer/markdown-extension/image-placeholder/hooks/use-placeholder-size-style.ts
+++ b/src/components/markdown-renderer/markdown-extension/image-placeholder/hooks/use-placeholder-size-style.ts
@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { CSSProperties } from 'react'
+import { useMemo } from 'react'
+import { calculatePlaceholderContainerSize } from '../utils/build-placeholder-size-css'
+
+/**
+ * Creates the style attribute for a placeholder container with width and height.
+ *
+ * @param width The wanted width
+ * @param height The wanted height
+ * @return The created style attributes
+ */
+export const usePlaceholderSizeStyle = (width?: string | number, height?: string | number): CSSProperties => {
+  return useMemo(() => {
+    const [convertedWidth, convertedHeight] = calculatePlaceholderContainerSize(width, height)
+
+    return {
+      width: `${convertedWidth}px`,
+      height: `${convertedHeight}px`
+    }
+  }, [height, width])
+}
--- a/src/components/markdown-renderer/markdown-extension/image-placeholder/image-placeholder-markdown-extension.ts
+++ b/src/components/markdown-renderer/markdown-extension/image-placeholder/image-placeholder-markdown-extension.ts
@ -0,0 +1,30 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { MarkdownExtension } from '../markdown-extension'
+import { addLineToPlaceholderImageTags } from './add-line-to-placeholder-image-tags'
+import type MarkdownIt from 'markdown-it/lib'
+import type { ComponentReplacer } from '../../replace-components/component-replacer'
+import { ImagePlaceholderReplacer } from './image-placeholder-replacer'
+
+/**
+ * A markdown extension that
+ */
+export class ImagePlaceholderMarkdownExtension extends MarkdownExtension {
+  public static readonly PLACEHOLDER_URL = 'https://'
+
+  constructor(private lineOffset: number) {
+    super()
+  }
+
+  configureMarkdownIt(markdownIt: MarkdownIt): void {
+    addLineToPlaceholderImageTags(markdownIt)
+  }
+
+  buildReplacers(): ComponentReplacer[] {
+    return [new ImagePlaceholderReplacer(this.lineOffset)]
+  }
+}
--- a/src/components/markdown-renderer/markdown-extension/image-placeholder/image-placeholder-replacer.tsx
+++ b/src/components/markdown-renderer/markdown-extension/image-placeholder/image-placeholder-replacer.tsx
@ -0,0 +1,44 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { NativeRenderer, NodeReplacement, SubNodeTransform } from '../../replace-components/component-replacer'
+import { ComponentReplacer } from '../../replace-components/component-replacer'
+import type { Element } from 'domhandler'
+import { ImagePlaceholder } from './image-placeholder'
+import { ImagePlaceholderMarkdownExtension } from './image-placeholder-markdown-extension'
+
+/**
+ * Replaces every image tag that has the {@link ImagePlaceholderMarkdownExtension.PLACEHOLDER_URL placeholder url} with the {@link ImagePlaceholder image placeholder element}.
+ */
+export class ImagePlaceholderReplacer extends ComponentReplacer {
+  private countPerSourceLine = new Map<number, number>()
+
+  constructor(private lineOffset: number) {
+    super()
+  }
+
+  reset(): void {
+    this.countPerSourceLine = new Map<number, number>()
+  }
+
+  replace(node: Element, subNodeTransform: SubNodeTransform, nativeRenderer: NativeRenderer): NodeReplacement {
+    if (node.name === 'img' && node.attribs && node.attribs.src === ImagePlaceholderMarkdownExtension.PLACEHOLDER_URL) {
+      const lineIndex = Number(node.attribs['data-line'])
+      const indexInLine = this.countPerSourceLine.get(lineIndex) ?? 0
+      this.countPerSourceLine.set(lineIndex, indexInLine + 1)
+      return (
+        <ImagePlaceholder
+          alt={node.attribs.alt}
+          title={node.attribs.title}
+          width={node.attribs.width}
+          height={node.attribs.height}
+          lineIndex={isNaN(lineIndex) ? undefined : lineIndex + this.lineOffset}
+          placeholderIndexInLine={indexInLine}
+        />
+      )
+    }
+  }
+}
--- a/src/components/markdown-renderer/markdown-extension/image-placeholder/image-placeholder.scss
+++ b/src/components/markdown-renderer/markdown-extension/image-placeholder/image-placeholder.scss
@ -0,0 +1,27 @@
+/*!
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+.image-drop {
+  @import "../../../../style/variables.light.scss";
+  border: 3px dashed $dark;
+
+  body.dark & {
+    @import "../../../../style/variables.dark.scss";
+    border-color: $dark;
+  }
+
+  border-radius: 3px;
+  transition: background-color 50ms, color 50ms;
+
+  .altText {
+    text-overflow: ellipsis;
+    flex: 1 1;
+    overflow: hidden;
+    width: 100%;
+    white-space: nowrap;
+    text-align: center;
+  }
+}
--- a/src/components/markdown-renderer/markdown-extension/image-placeholder/image-placeholder.tsx
+++ b/src/components/markdown-renderer/markdown-extension/image-placeholder/image-placeholder.tsx
@ -0,0 +1,112 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import React, { useCallback, useMemo, useRef, useState } from 'react'
+import { Button } from 'react-bootstrap'
+import { Trans, useTranslation } from 'react-i18next'
+import { ForkAwesomeIcon } from '../../../common/fork-awesome/fork-awesome-icon'
+import './image-placeholder.scss'
+import { acceptedMimeTypes } from '../../../common/upload-image-mimetypes'
+import { useOnImageUpload } from './hooks/use-on-image-upload'
+import { usePlaceholderSizeStyle } from './hooks/use-placeholder-size-style'
+
+export interface PlaceholderImageFrameProps {
+  alt?: string
+  title?: string
+  width?: string | number
+  height?: string | number
+  lineIndex?: number
+  placeholderIndexInLine?: number
+}
+
+/**
+ * Shows a placeholder for an actual image with the possibility to upload images via button or drag'n'drop.
+ *
+ * @param alt The alt text of the image. Will be shown in the placeholder
+ * @param title The title text of the image. Will be shown in the placeholder
+ * @param width The width of the placeholder
+ * @param height The height of the placeholder
+ * @param lineIndex The index of the line in the markdown content where the placeholder is defined
+ * @param placeholderIndexInLine The index of the placeholder in the markdown line
+ */
+export const ImagePlaceholder: React.FC<PlaceholderImageFrameProps> = ({
+  alt,
+  title,
+  width,
+  height,
+  lineIndex,
+  placeholderIndexInLine
+}) => {
+  useTranslation()
+  const fileInputReference = useRef<HTMLInputElement>(null)
+  const onImageUpload = useOnImageUpload(lineIndex, placeholderIndexInLine)
+
+  const [showDragStatus, setShowDragStatus] = useState(false)
+
+  const onDropHandler = useCallback(
+    (event: React.DragEvent<HTMLSpanElement>) => {
+      event.preventDefault()
+      if (event?.dataTransfer?.files?.length > 0) {
+        onImageUpload(event.dataTransfer.files[0])
+      }
+    },
+    [onImageUpload]
+  )
+
+  const onDragOverHandler = useCallback((event: React.DragEvent<HTMLSpanElement>) => {
+    event.preventDefault()
+    setShowDragStatus(true)
+  }, [])
+
+  const onDragLeave = useCallback(() => {
+    setShowDragStatus(false)
+  }, [])
+
+  const onChangeHandler = useCallback(
+    (event: React.ChangeEvent<HTMLInputElement>) => {
+      const fileList = event.target.files
+      if (!fileList || fileList.length < 1) {
+        return
+      }
+      onImageUpload(fileList[0])
+    },
+    [onImageUpload]
+  )
+
+  const uploadButtonClicked = useCallback(() => fileInputReference.current?.click(), [])
+  const containerStyle = usePlaceholderSizeStyle(width, height)
+
+  const containerDragClasses = useMemo(() => (showDragStatus ? 'bg-primary text-white' : 'text-dark'), [showDragStatus])
+
+  return (
+    <span
+      className={`image-drop d-inline-flex flex-column align-items-center ${containerDragClasses} p-1`}
+      style={containerStyle}
+      onDrop={onDropHandler}
+      onDragOver={onDragOverHandler}
+      onDragLeave={onDragLeave}>
+      <input
+        type='file'
+        className='d-none'
+        accept={acceptedMimeTypes}
+        onChange={onChangeHandler}
+        ref={fileInputReference}
+      />
+      <div className={'align-items-center flex-column justify-content-center flex-fill d-flex'}>
+        <div className={'d-flex flex-column'}>
+          <span className='my-2'>
+            <Trans i18nKey={'editor.embeddings.placeholderImage.placeholderText'} />
+          </span>
+          <span className={'altText'}>{alt ?? title ?? ''}</span>
+        </div>
+      </div>
+      <Button size={'sm'} variant={'primary'} onClick={uploadButtonClicked}>
+        <ForkAwesomeIcon icon={'upload'} fixedWidth={true} className='my-2' />
+        <Trans i18nKey={'editor.embeddings.placeholderImage.upload'} className='my-2' />
+      </Button>
+    </span>
+  )
+}
--- a/src/components/markdown-renderer/markdown-extension/image-placeholder/utils/build-placeholder-size-css.test.ts
+++ b/src/components/markdown-renderer/markdown-extension/image-placeholder/utils/build-placeholder-size-css.test.ts
@ -0,0 +1,67 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { calculatePlaceholderContainerSize, parseSizeNumber } from './build-placeholder-size-css'
+
+describe('parseSizeNumber', () => {
+  it('undefined', () => {
+    expect(parseSizeNumber(undefined)).toBe(undefined)
+  })
+  it('zero as number', () => {
+    expect(parseSizeNumber(0)).toBe(0)
+  })
+  it('positive number', () => {
+    expect(parseSizeNumber(234)).toBe(234)
+  })
+  it('negative number', () => {
+    expect(parseSizeNumber(-123)).toBe(-123)
+  })
+  it('zero as string', () => {
+    expect(parseSizeNumber('0')).toBe(0)
+  })
+  it('negative number as string', () => {
+    expect(parseSizeNumber('-123')).toBe(-123)
+  })
+  it('positive number as string', () => {
+    expect(parseSizeNumber('345')).toBe(345)
+  })
+  it('positive number with px as string', () => {
+    expect(parseSizeNumber('456px')).toBe(456)
+  })
+  it('negative number with px as string', () => {
+    expect(parseSizeNumber('-456px')).toBe(-456)
+  })
+})
+
+describe('calculatePlaceholderContainerSize', () => {
+  it('width undefined | height undefined', () => {
+    expect(calculatePlaceholderContainerSize(undefined, undefined)).toStrictEqual([500, 200])
+  })
+  it('width 200 | height undefined', () => {
+    expect(calculatePlaceholderContainerSize(200, undefined)).toStrictEqual([200, 80])
+  })
+  it('width undefined | height 100', () => {
+    expect(calculatePlaceholderContainerSize(undefined, 100)).toStrictEqual([250, 100])
+  })
+  it('width "0" | height 0', () => {
+    expect(calculatePlaceholderContainerSize('0', 0)).toStrictEqual([0, 0])
+  })
+  it('width 0 | height "0"', () => {
+    expect(calculatePlaceholderContainerSize(0, '0')).toStrictEqual([0, 0])
+  })
+  it('width -345 | height 234', () => {
+    expect(calculatePlaceholderContainerSize(-345, 234)).toStrictEqual([-345, 234])
+  })
+  it('width 345 | height -234', () => {
+    expect(calculatePlaceholderContainerSize(345, -234)).toStrictEqual([345, -234])
+  })
+  it('width "-345" | height -234', () => {
+    expect(calculatePlaceholderContainerSize('-345', -234)).toStrictEqual([-345, -234])
+  })
+  it('width -345 | height "-234"', () => {
+    expect(calculatePlaceholderContainerSize(-345, '-234')).toStrictEqual([-345, -234])
+  })
+})
--- a/src/components/markdown-renderer/markdown-extension/image-placeholder/utils/build-placeholder-size-css.ts
+++ b/src/components/markdown-renderer/markdown-extension/image-placeholder/utils/build-placeholder-size-css.ts
@ -0,0 +1,66 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+const regex = /^(-?[0-9]+)px$/
+
+/**
+ * Inspects the given value and checks if it is a number or a pixel size string.
+ *
+ * @param value The value to check
+ * @return the number representation of the string or undefined if it couldn't be parsed
+ */
+export const parseSizeNumber = (value: string | number | undefined): number | undefined => {
+  if (value === undefined) {
+    return undefined
+  }
+
+  if (typeof value === 'number') {
+    return value
+  }
+
+  const regexMatches = regex.exec(value)
+  if (regexMatches !== null) {
+    if (regexMatches && regexMatches.length > 1) {
+      return parseInt(regexMatches[1])
+    } else {
+      return undefined
+    }
+  }
+
+  if (!Number.isNaN(value)) {
+    return parseInt(value)
+  }
+}
+
+/**
+ * Calculates the final width and height for a placeholder container.
+ * Every parameter that is empty will be defaulted using a 500:200 ratio.
+ *
+ * @param width The wanted width
+ * @param height The wanted height
+ * @return the calculated size
+ */
+export const calculatePlaceholderContainerSize = (
+  width: string | number | undefined,
+  height: string | number | undefined
+): [width: number, height: number] => {
+  const defaultWidth = 500
+  const defaultHeight = 200
+  const ratio = defaultWidth / defaultHeight
+
+  const convertedWidth = parseSizeNumber(width)
+  const convertedHeight = parseSizeNumber(height)
+
+  if (convertedWidth === undefined && convertedHeight !== undefined) {
+    return [convertedHeight * ratio, convertedHeight]
+  } else if (convertedWidth !== undefined && convertedHeight === undefined) {
+    return [convertedWidth, convertedWidth * (1 / ratio)]
+  } else if (convertedWidth !== undefined && convertedHeight !== undefined) {
+    return [convertedWidth, convertedHeight]
+  } else {
+    return [defaultWidth, defaultHeight]
+  }
+}
--- a/src/components/markdown-renderer/markdown-extension/linemarker/linemarker-markdown-extension.ts
+++ b/src/components/markdown-renderer/markdown-extension/linemarker/linemarker-markdown-extension.ts
@ -17,7 +17,7 @@ import type MarkdownIt from 'markdown-it'
 export class LinemarkerMarkdownExtension extends MarkdownExtension {
  public static readonly tagName = 'app-linemarker'

-  constructor(private onLineMarkers?: (lineMarkers: LineMarkers[]) => void, private lineOffset?: number) {
+  constructor(private lineOffset: number, private onLineMarkers?: (lineMarkers: LineMarkers[]) => void) {
    super()
  }

--- a/src/components/markdown-renderer/markdown-extension/task-list/task-list-markdown-extension.ts
+++ b/src/components/markdown-renderer/markdown-extension/task-list/task-list-markdown-extension.ts
@ -15,7 +15,7 @@ import markdownItTaskLists from '@hedgedoc/markdown-it-task-lists'
 * Adds support for interactive checkbox lists to the markdown rendering using the github checklist syntax.
 */
 export class TaskListMarkdownExtension extends MarkdownExtension {
-  constructor(private frontmatterLinesToSkip?: number, private onTaskCheckedChange?: TaskCheckedChangeHandler) {
+  constructor(private frontmatterLinesToSkip: number, private onTaskCheckedChange?: TaskCheckedChangeHandler) {
    super()
  }

--- a/src/components/markdown-renderer/markdown-extension/task-list/task-list-replacer.tsx
+++ b/src/components/markdown-renderer/markdown-extension/task-list/task-list-replacer.tsx
@ -18,10 +18,10 @@ export type TaskCheckedChangeHandler = (lineInMarkdown: number, checked: boolean
 export class TaskListReplacer extends ComponentReplacer {
  onTaskCheckedChange?: (lineInMarkdown: number, checked: boolean) => void

-  constructor(frontmatterLinesToSkip?: number, onTaskCheckedChange?: TaskCheckedChangeHandler) {
+  constructor(frontmatterLinesToSkip: number, onTaskCheckedChange?: TaskCheckedChangeHandler) {
    super()
    this.onTaskCheckedChange = (lineInMarkdown, checked) => {
-      if (onTaskCheckedChange === undefined || frontmatterLinesToSkip === undefined) {
+      if (onTaskCheckedChange === undefined) {
        return
      }
      onTaskCheckedChange(frontmatterLinesToSkip + lineInMarkdown, checked)
--- a/src/components/markdown-renderer/markdown-extension/upload-indicating-image-frame/upload-indicating-frame.tsx
+++ b/src/components/markdown-renderer/markdown-extension/upload-indicating-image-frame/upload-indicating-frame.tsx
@ -0,0 +1,37 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import React from 'react'
+import { ForkAwesomeIcon } from '../../../common/fork-awesome/fork-awesome-icon'
+import { usePlaceholderSizeStyle } from '../image-placeholder/hooks/use-placeholder-size-style'
+import { Trans, useTranslation } from 'react-i18next'
+
+export interface UploadIndicatingFrameProps {
+  width?: string | number
+  height?: string | number
+}
+
+/**
+ * Shows a placeholder frame for images that are currently uploaded.
+ *
+ * @param width The frame width
+ * @param height The frame height
+ */
+export const UploadIndicatingFrame: React.FC<UploadIndicatingFrameProps> = ({ width, height }) => {
+  const containerStyle = usePlaceholderSizeStyle(width, height)
+  useTranslation()
+
+  return (
+    <span
+      className='image-drop d-inline-flex flex-column align-items-center justify-content-center bg-primary text-white p-4'
+      style={containerStyle}>
+      <span className={'h1 border-bottom-0 my-2'}>
+        <Trans i18nKey={'renderer.uploadIndicator.uploadMessage'} />
+      </span>
+      <ForkAwesomeIcon icon={'cog'} size={'5x'} fixedWidth={true} className='my-2 fa-spin' />
+    </span>
+  )
+}
--- a/src/components/markdown-renderer/markdown-extension/upload-indicating-image-frame/upload-indicating-image-frame-markdown-extension.ts
+++ b/src/components/markdown-renderer/markdown-extension/upload-indicating-image-frame/upload-indicating-image-frame-markdown-extension.ts
@ -0,0 +1,18 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { MarkdownExtension } from '../markdown-extension'
+import type { ComponentReplacer } from '../../replace-components/component-replacer'
+import { UploadIndicatingImageFrameReplacer } from './upload-indicating-image-frame-replacer'
+
+/**
+ * A markdown extension that shows {@link UploadIndicatingFrame} for images that are getting uploaded.
+ */
+export class UploadIndicatingImageFrameMarkdownExtension extends MarkdownExtension {
+  buildReplacers(): ComponentReplacer[] {
+    return [new UploadIndicatingImageFrameReplacer()]
+  }
+}
--- a/src/components/markdown-renderer/markdown-extension/upload-indicating-image-frame/upload-indicating-image-frame-replacer.tsx
+++ b/src/components/markdown-renderer/markdown-extension/upload-indicating-image-frame/upload-indicating-image-frame-replacer.tsx
@ -0,0 +1,23 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { NativeRenderer, NodeReplacement, SubNodeTransform } from '../../replace-components/component-replacer'
+import { ComponentReplacer } from '../../replace-components/component-replacer'
+import type { Element } from 'domhandler'
+import { UploadIndicatingFrame } from './upload-indicating-frame'
+
+const uploadIdRegex = /^upload-(.+)$/
+
+/**
+ * Replaces an image tag whose url is an upload-id with the {@link UploadIndicatingFrame upload indicating frame}.
+ */
+export class UploadIndicatingImageFrameReplacer extends ComponentReplacer {
+  replace(node: Element, subNodeTransform: SubNodeTransform, nativeRenderer: NativeRenderer): NodeReplacement {
+    if (node.name === 'img' && uploadIdRegex.test(node.attribs.src)) {
+      return <UploadIndicatingFrame width={node.attribs.width} height={node.attribs.height} />
+    }
+  }
+}
--- a/src/components/markdown-renderer/replace-components/component-replacer.ts
+++ b/src/components/markdown-renderer/replace-components/component-replacer.ts
@ -49,6 +49,13 @@ export abstract class ComponentReplacer {
    return node.children.map((value, index) => subNodeTransform(value, index))
  }

+  /**
+   * Should be used to reset the replacers internal state before rendering.
+   */
+  public reset(): void {
+    // left blank for overrides
+  }
+
  /**
   * Checks if the current node should be altered or replaced and does if needed.
   *
--- a/src/components/markdown-renderer/slideshow-markdown-renderer.tsx
+++ b/src/components/markdown-renderer/slideshow-markdown-renderer.tsx
@ -45,7 +45,7 @@ export const SlideshowMarkdownRenderer: React.FC<SlideshowMarkdownRendererProps
    baseUrl,
    undefined,
    useMemo(() => [new RevealMarkdownExtension()], []),
-    lineOffset,
+    lineOffset ?? 0,
    onTaskCheckedChange,
    onImageClick,
    onTocChange
--- a/src/components/markdown-renderer/utils/node-to-react-transformer.tsx
+++ b/src/components/markdown-renderer/utils/node-to-react-transformer.tsx
@ -31,6 +31,13 @@ export class NodeToReactTransformer {
    this.replacers = replacers
  }

+  /**
+   * Resets all replacers before rendering.
+   */
+  public resetReplacers(): void {
+    this.replacers.forEach((replacer) => replacer.reset())
+  }
+
  /**
   * Converts the given {@link Node} to a react element.
   *
--- a/src/components/render-page/window-post-message-communicator/rendering-message.ts
+++ b/src/components/render-page/window-post-message-communicator/rendering-message.ts
@ -19,7 +19,8 @@ export enum CommunicationMessageType {
  SET_BASE_CONFIGURATION = 'SET_BASE_CONFIGURATION',
  GET_WORD_COUNT = 'GET_WORD_COUNT',
  ON_WORD_COUNT_CALCULATED = 'ON_WORD_COUNT_CALCULATED',
-  SET_FRONTMATTER_INFO = 'SET_FRONTMATTER_INFO'
+  SET_FRONTMATTER_INFO = 'SET_FRONTMATTER_INFO',
+  IMAGE_UPLOAD = 'IMAGE_UPLOAD'
 }

 export interface NoPayloadMessage {
@ -37,6 +38,14 @@ export interface ImageDetails {
  title?: string
 }

+export interface ImageUploadMessage {
+  type: CommunicationMessageType.IMAGE_UPLOAD
+  dataUri: string
+  fileName: string
+  lineIndex?: number
+  placeholderIndexInLine?: number
+}
+
 export interface SetBaseUrlMessage {
  type: CommunicationMessageType.SET_BASE_CONFIGURATION
  baseConfiguration: BaseConfiguration
@ -100,6 +109,7 @@ export type CommunicationMessages =
  | SetFrontmatterInfoMessage
  | OnHeightChangeMessage
  | OnWordCountCalculatedMessage
+  | ImageUploadMessage

 export type EditorToRendererMessageType =
  | CommunicationMessageType.SET_MARKDOWN_CONTENT
@ -118,6 +128,7 @@ export type RendererToEditorMessageType =
  | CommunicationMessageType.IMAGE_CLICKED
  | CommunicationMessageType.ON_HEIGHT_CHANGE
  | CommunicationMessageType.ON_WORD_COUNT_CALCULATED
+  | CommunicationMessageType.IMAGE_UPLOAD

 export enum RendererType {
  DOCUMENT = 'document',
--- a/src/redux/note-details/methods.ts
+++ b/src/redux/note-details/methods.ts
@ -7,6 +7,7 @@
 import { store } from '..'
 import type { NoteDto } from '../../api/notes/types'
 import type {
+  ReplaceInMarkdownContentAction,
  SetNoteDetailsFromServerAction,
  SetNoteDocumentContentAction,
  UpdateNoteTitleByFirstHeadingAction,
@ -49,6 +50,7 @@ export const updateNoteTitleByFirstHeading = (firstHeading?: string): void => {

 /**
 * Changes a checkbox state in the note document content. Triggered when a checkbox in the rendering is clicked.
+ *
 * @param lineInDocumentContent The line in the document content to change.
 * @param checked true if the checkbox is checked, false otherwise.
 */
@ -59,3 +61,17 @@ export const setCheckboxInMarkdownContent = (lineInDocumentContent: number, chec
    changedLine: lineInDocumentContent
  } as UpdateTaskListCheckboxAction)
 }
+
+/**
+ * Replaces a string in the markdown content in the global application state.
+ *
+ * @param replaceable The string that should be replaced
+ * @param replacement The replacement for the replaceable
+ */
+export const replaceInMarkdownContent = (replaceable: string, replacement: string): void => {
+  store.dispatch({
+    type: NoteDetailsActionType.REPLACE_IN_MARKDOWN_CONTENT,
+    placeholder: replaceable,
+    replacement
+  } as ReplaceInMarkdownContentAction)
+}
--- a/src/redux/note-details/reducer.ts
+++ b/src/redux/note-details/reducer.ts
@ -28,11 +28,29 @@ export const NoteDetailsReducer: Reducer<NoteDetails, NoteDetailsActions> = (
      return buildStateFromServerDto(action.dto)
    case NoteDetailsActionType.UPDATE_TASK_LIST_CHECKBOX:
      return buildStateFromTaskListUpdate(state, action.changedLine, action.checkboxChecked)
+    case NoteDetailsActionType.REPLACE_IN_MARKDOWN_CONTENT:
+      return buildStateFromDocumentContentReplacement(state, action.placeholder, action.replacement)
    default:
      return state
  }
 }

+/**
+ * Builds a {@link NoteDetails} redux state with a modified markdown content.
+ *
+ * @param state The previous redux state
+ * @param replaceable The string that should be replaced in the old markdown content
+ * @param replacement The string that should replace the replaceable
+ * @return An updated {@link NoteDetails} redux state
+ */
+const buildStateFromDocumentContentReplacement = (
+  state: NoteDetails,
+  replaceable: string,
+  replacement: string
+): NoteDetails => {
+  return buildStateFromMarkdownContentUpdate(state, state.markdownContent.replaceAll(replaceable, replacement))
+}
+
 /**
 * Builds a {@link NoteDetails} redux state from a DTO received as an API response.
 * @param dto The first DTO received from the API containing the relevant information about the note.
--- a/src/redux/note-details/types.ts
+++ b/src/redux/note-details/types.ts
@ -11,7 +11,8 @@ export enum NoteDetailsActionType {
  SET_DOCUMENT_CONTENT = 'note-details/content/set',
  SET_NOTE_DATA_FROM_SERVER = 'note-details/data/server/set',
  UPDATE_NOTE_TITLE_BY_FIRST_HEADING = 'note-details/update-note-title-by-first-heading',
-  UPDATE_TASK_LIST_CHECKBOX = 'note-details/update-task-list-checkbox'
+  UPDATE_TASK_LIST_CHECKBOX = 'note-details/update-task-list-checkbox',
+  REPLACE_IN_MARKDOWN_CONTENT = 'note-details/replace-in-markdown-content'
 }

 export type NoteDetailsActions =
@ -19,6 +20,7 @@ export type NoteDetailsActions =
  | SetNoteDetailsFromServerAction
  | UpdateNoteTitleByFirstHeadingAction
  | UpdateTaskListCheckboxAction
+  | ReplaceInMarkdownContentAction

 /**
 * Action for updating the document content of the currently loaded note.
@ -52,3 +54,9 @@ export interface UpdateTaskListCheckboxAction extends Action<NoteDetailsActionTy
  changedLine: number
  checkboxChecked: boolean
 }
+
+export interface ReplaceInMarkdownContentAction extends Action<NoteDetailsActionType> {
+  type: NoteDetailsActionType.REPLACE_IN_MARKDOWN_CONTENT
+  placeholder: string
+  replacement: string
+}