

Each fediverse instance is ranked separately that’s the biggest issue. Each specific post is ranked based on the instance of the community its from due to content origin links. So the same post isn’t ranked separately but each instance is only ranked based on the posts to its own communities.
Use a script to copy over the photos from the public to the private. I assume the software ur using has a database to store all the metadata. U can set up one of ur servers as a master db and mirror that through a variety of tools to the other location. I think u would need to set the master db as the one on ur private machine (as it has all the content) and mirror that to the public. I’m not sure how ur software will handle having metadata for images it doesn’t actually have.
Their might be some way to do bidirectional db sync. Or perhaps run the db on the public and connect ur private to that db. So u would have 2 services running off the same db (and syncing files back to the private as necessary).
I use Immich as my image management and u can point it to any db service u want.
Edit: u might be able to do some custom delivery config in nginx or similar to serve the content itself from the public and if that fails serve the content from the private (u would need to make the private public for this).