Whether AI training in general is fair use and whether an AI that spits out a verbatim copy of something from the training data has produced an infringing copy are two different questions.

If there is some copyrighted art in the background in a scene from a movie, maybe that's fair use. If you take a high resolution copy of the movie, extract only the art from the background and want to start distributing that on its own, what do you expect then?