There probably is a case to be made for at least prohibiting the use of phrases like "a painting by $ARTIST" as a trademark violation (particularly if it is a r

There probably is a case to be made for at least prohibiting the use of phrases like "a painting by $ARTIST" as a trademark violation (particularly if it is a registered trademark) since what is produced is not, actually, a work by the artist named, but that would still permit the use of prompts like "a painting in the style of $ARTIST". Even if you could prohibit the use of an artist's name entirely, that wouldn't eliminate the use of their actual style per-se, users would just have to refer to it some other way, such as using a prompt like "dark necrofetishist biomechanoid style" instead of "in the style of H. R. Giger".