What can law do to stop nude celebrity ‘art’ photos from floating around?

Apparently, not much.

[T]he fact that the photos were obtained by obviously criminal activity does not itself prevent publishers or artists from using the photos. This may seem counterintuitive — after all, if a thief breaks in to your house and steals a piece of your jewelry, an artist cannot then buy the stolen jewelry from the thief and display it as “artistic commentary” on an “individual’s security in this age of crime.” As appealing an analogy as this might be, it does not work here.