We need some image processing for e.g.
- Thumbnails, e.g. in tables see #1280
- Previews, e.g. downsize images in entity views when too big
- Slideshows, again downsizing if images are too big
- An original file should be kept and be available
- Do we process the images on the fly or in a batch job or after uploaded and store them for later use, ...
- Alternatives for projects we know in advance that they will have mainly large images (e.g. scans), should we consider something like an IIIF API?