I used the same photo as reference that Shepard Fairey used for his famous Hope poster. Certainly one of the most iconic graphic images created in the last 20 years. Once it was clear that the image was going to have a continuing cultural and historical impact the AP, who own the rights to the original photograph, insisted on getting a cut of the action. Fairey sued them on the grounds of fair use and the parties ultimately settled before going to trial.
Fairey and I both went to RISD. I don't know him, he's younger than me. But we both learned the same thing: that all images are fair game. Everything is in the mix. As an artist I can do whatever I want. When I interpret an image, I am making a new thing. It's mine.
The AP can go fuck off.