I folded. Like an ancient, sun-faded lawn chair.
I wanted a Professor Brothers avatar, but the detail was a bit much for 50x50 pixels.
As a compromise, I've increased static images (JPGs) to 200x200 pixels, and animations (GIFs) to 150x150 pixels. Size constraints still exist, and are the same (less than 1MB upload for each). I'm still letting you have 100% image quality on JPGs. GIFs I can't speak for.
I'm still limiting the size on each thread / item to 50x50px, but I'm displaying full size when you click on a user's page.
Go ahead and re-upload your images if you want to have the higher quality version displayed with your user page. I might in the future figure out a way to display them larger on the threads, but it'll have to be a way that doesn't disrupt the content of the message.