You can use [Amazon S3](https://aws.amazon.com/s3/) or any other S3-compatible storage (like [MinIO](https://min.io) or [Ceph Object Gateway](https://docs.ceph.com/en/latest/radosgw/)) to handle your image uploads in HedgeDoc.
Your S3 bucket must be configured to be writeable.
You just add the following lines to your configuration:
<small>(with the appropriate substitution for `<ACCESS_KEY>`, `<SECRET_KEY>`, `<BUCKET>`, and `<ENDPOINT>` of course)</small>