School: Purple Rain...of Copyright Infringement
The rights provided by the Copyright Act last for a relatively long time, but they are also more porous than, say, patent rights. Case in point:
Now, Prince's cover version of Radiohead's "Creep" weaves in Hendrix and Marvin Gaye, but it's still a cover. After it was uploaded onto YouTube, Prince's label (and quite possibly Prince's lawyer, who spoke to us when we began law school here at UF) requested it be taken down. I heard even Radiohead couldn't watch the video. For my part, I'm hoping a grainy, low-quality video of a performance that is posted on a noncommercial blog for the purposes of illustrating a current legal controversy counts as fair use, but who knows in this day and age?
Assuming Prince had permission to use the song, though, I suppose this new performance is as much his as it is Radiohead's - at least the parts where Prince was improvising or combining various musical elements. I can see how one could argue that concert bootlegs like this hurt the market for future concert DVDs, but it seems like a fairly small problem when the man's playing in packed arenas and selling albums hand over fist. It's definitely sending the wrong message to fans, at least.