yeah, yogurt's suggestion was really good. heres how it could work:

you already see the upload when you submit it, but before it is actually submitted, you should get the pm with the image, and have to confirm that this image is what you wish to submit. Have them wait a few seconds while the background changes color (to make transparency issues easier to see) and then they can accept it.

ideally for animations they (submitter) would have to sit through the entire thing themselves and make sure everything is right in-game.