I thought I'd add some facts, observations and opinions of my own.
- The poster is not a photograph and has not been altered in Photoshop with a simple click of a mouse, as people on the internet who know absolutely nothing about Photoshop are claiming. It is a new illustration based on a photograph that was most likely created in Illustrator.
- Some people are defending him on the basis that he didn't make money off of it. It doesn't matter either way. You are allowed to profit off of your own work, which this is. You are also allowed to make derivative works, which this could be considered. Marcel Duchamp famously drew a mustache, goatee and caption on the Mona Lisa and created something different with an entirely new context. (In this case mocking fine art and its rich admirers.)
- The photographer and the AP deserve no credit or compensation. He should mention it is based off of a photograph only when talking about the creative process of the piece. (Fairey has done this even though it's self-evident he used a photograph.)
- These types of things have been hashed out in the art world and in courts for quite a while. His work clearly and squarely falls into the category of fair use. Any lawsuit would be completely frivolous.