Maybe he's suing for emotional damage. He grew up with an inferior complex because of his size portrayed ... 
The emotional damage is he identifies as she making the cover a painful reminder of societies oppression of trans yada yada whatever. It wants its cut, okay?
Well look if my weenie was on the cover of one of the most popular and praised albums of all time I’d probably want a cut too. Just saying.
The production company/photographer is responsible for getting the release signed, yet I believe all those named in this case can be sued. Really lame on their part, weren't the kid's parents there?

But it seems that he's had years of fun being the cover child. Until he met the lawyer.