Just as I come to mention something, I see you're taking suggestions.
So, here's for my most basical recommendation: SSL
I have some old turboimagehost links here and there, and they force the mixed content warning, it's a pity. I tried replacing http with https but the img src links broke, so apparently it's not yet implemented on your side.
Other than that, what you would gain to add would be a gallery feature, or call it album if you like. An uploader would upload a set of images, and no matter which image of the set the internet visitor ends up opening, he would have a navigation menu to view the index of all the thumbnails, plus links for the previous/next image. Keyboard shortcuts left/right taken in charge, and tapping for mobile visitors ofc.
Think of the advantage to people who want to upload comics (you offer them the entire "read online" feature, they don't have to scratch their heads and ask themselves how to self-host the hell out of it) and video previews (much greater chance to view the other previews uploaded by the OP, increases likelyhood it seduces the visitor.
Also, your forum catpcha is nightmare-class, maybe it's time to join the forces of evil and add recaptcha instead.
And a less neolithic looking entry page on turboimagehost, but that is kinda needless to mention, good luck out there
