I think it's not as clear as you claim and more like a big gray area, like a lot of fan art out there. Some images in the dataset themselves might be infringing

I think it's not as clear as you claim and more like a big gray area, like a lot of fan art out there. Some images in the dataset themselves might be infringing on some other publisher's rights. On the other hand some artists knowingly submit their original art to the image boards. Where exactly is the point between a derivative work and an original work that was inspired by something? A lot of fan art I see clearly depicts a character from some franchise in a style that is close to the original, but say, in a new pose or setting. Is that copyright infringement? Trademark infringement? What if it's an original character in the exact style from the franchise? Some artists sell this kind of art as their own at conventions and will aggressively try to remove reposts on the web. On the other extreme, I've seen other artists tag any fan art remotely connected with some franchise with "copyright by <franchise owner>" and denounce any rights to their work.