> But including your art in the training data is fair use
The four factors of fair use in the US:
> the purpose and character of your use
Commercial, for-profit. Not scholarship, not research, not commentary, not parody, etc.
> the nature of the copyrighted work
Absolutely everything. Artistic, creative, not purely factual.
> the amount and substantiality of the portion taken, and
All of it, from everyone.
> the effect of the use upon the potential market.
Directly competing with those whose data was copied.
3 and 4 are what that argument is based on, I believe. 3) on the basis that the output is not _reproduced_, and 4) on similar grounds that output that's just not at all the same as the input data isn't affecting the market for the original image (I think this is the more debatable one, but in general the existing cases have struggled at the early stages because the plaintiffs have not been able to actually point to output that is a copy of their part of the input, and this does actually matter).
> the amount and substantiality of the portion taken, and
> All of it, from everyone.
Yea I'd like to see how drawing two circles violates the copyright of drawing one circle!