Here is an obvious fake.
I wanted to share this just because it's amusing. The signature looks like lots of other obvious fakes, but it's underscored by the fact that the Kodak logo on the back of the print is a logo that didn't exist until 2006. Whoops. This is the second Kurt Cobain "autograph" that I've seen on this sort of paper.
Here is a page on the history of Kodak logos.
It's good info for any autograph collector.

