It's important to note, this is not a faithful representation once you look at it closely. The text is always mangled into nonsense and things like brands or logos are never close enough to be even a passing likeness.
This is no different from a painter using a photograph of a subject to create a portrait, which is subsequently sold.
Or recording a song on the radio to learn to play the guitar, then using that song as inspiration to write a new song.
That being said, I suspect they are removing all watermarked images from training databases right now.