Not that I’m the person to do it, mind you, but for your own safety and liability purposes I advise caution allowing uploaded images to be used.

As in, it may have the potential for content that you find disturbing, inappropriate, or illegal. Between stories/concepts like NEDM and Rule 34, the potential for misuse, if unregulated, could be exploited by an opportunistic bad actor.

At the bare minimum, use of Copyrighted material could foreseeably result in a view that your project, even at the free stage, is a form of enabling unauthorized derivative works…and result in litigation.