Have you ever been to the market part of a fan convention? People sell a shitload of copywrited art there, and no one really cared about that. The fact that you wouldnt be able to use a lot of those things commercially doesnt stop people from buying them.

Edit: Also if you sold that database I wouldnt buy it because I dont give a shit about the images the machine was trained on, I give a shit about the art I ask it to make for me, which it consistently does exactly the way I want. Is commissioning humans illegal now?