How about Lensdump. Doesn't have a gallery, you just share the URL, but the nice thing is there's an auto-delete feature. Guess that would more handy if you were sharing pictures to friends/family, and not so much a forum/board, but still a nice feature to have.

Sorry for necrobumping this thread and you may have already found a solution, but you might try Picsur. It's an open-source, self-hosted Imgur clone. The self-hosted aspect might not be exactly what you're looking for, but I did set it up in docker and it worked well and was a simple process.

The development seems to have slowed down a bit, but it does seem feature complete.

I don't understand. What's the point of posting private photos to a federated service? Just use Imgur.

"When all you have is a hammer, every problem looks like a nail."