What I feel is missing from the practical suggestions section: why cache images at all? They should be stored on the server they were uploaded to, and nowhere else. The image URL would be attached to the post, and could then be used by clients to fetch the image from the original server.
I thought lemmy did this, but it seems not (any more?).
I’m pretty sure they try to upstream as much as possible. They have made some pretty large upstream contributions which started out in their own fork.