until ai actually starts procedurally creating images with bespoke tools rather than blending pixels it will in fact be fairly easy to distinguish a made image from a generated one for the same reasons you can usually tell if someone painted over 3d or used a photo base. ai has a lot of dalle-isms and artifacts that i cannot see going away any time soon. on top of that you could simply require posted images to come with a process timelapse. heavypaint and a few other pieces of software already store those in the png data.