If I were doing this, I would have the system generate the image, and then I would have it run a secondary estimate saying "probability that this is a picture of [list of characters that Disney has given us reference input for]". If the picture has a "looks like Spiderman" score greater than X, then block it. EDIT - To answer the question, I'm guessing Disney provided a reference set of copyrighted images and characters, and somehow forgot Indiana Jones.

There seemed to be so many that weren't blocked, which is curious.