Fan art is generally protected because of a rule called "fair use", which allows people to use copyrighted work without permission. For example, if you briefly quote a book, the author won't have success if they go after you for copying from their book, even though you clearly did. Generally speaking, a person making fan art and not selling it is going to be protected under fair use. The law wants creators to have control of the thing they created, but we all live in a shared culture and we all deserve to participate in the art we experience, so there's some wiggle room, and this has been the case long before AI was a thing.
What these AI companies are doing, on the other hand... well, it hasn't really been tested in court yet, but they're doing a lot more than single images or brief quotes, and they're doing it for money, so they'll likely have some work to do.
Those images in the mirror are already perfect replicas of us, we need to be ready for when they figure out how to move on their own and get out from behind the glass or we'll really be screwed. If you give my """non-profit""" a trillion dollars we'll get right to work on the research into creating more capable mirror monsters so that we can control them instead.