I am not arguing a general case; I'm arguing specifically that Maisel should not have complained, let alone started a lawsuit, about this specific use of one of his works, in part because he is in the position to do so. He can let a thousand derivative suns, making a few handfuls of people happy each time, bloom without any negative effects for him.
But really, if this guy had used a picture by your girlfriend as the cover art, she would have been pissed? Why? Because a couple of dozen people now have a CD with some version of her art on the cover? Because some guy on the internet has that version on his website? I don't understand that at all. Even unknown artists are supremely unlikely to suffer any negative consequences as a result of this tiny project using one of their images. It isn't like this is a serious commercial effort: it was born out of love, not out of a quest for cash.