Shepard Fairey: Plagiarism Or Art?

I would think many artists use photo or other types of reference at some time or another. It's pretty standard.

But what happens when you have a case like Shepard Fairey's Obama poster -- where not only was extensive referencing of an Associated Press photo used, but the poster itself becomes an international phenomenon?

Is it plagiarism or art? Is it fair use? Did Fairey "transform" the image enough to the point where it has become a separate entity? If he makes money off the image, does the original AP photographer deserve a cut, as well?

Here's another example. The following work is from edgy street artist Rupert Endive:

"Super Heavy Sex Machine No. 9/CRAZE" by Rupert Endive, 2003.
Photograph and Sharpie.

Endive's main "hook" is to put graffiti tags and other sorts of defacement on posters, magazine advertisements, and newspaper headlines. When Endive sells his work, does he owe a cut to the original producers of the material he has "defaced"? Or, because he has added his own ideas to the material -- thus rendering them ironic -- has he created a whole new work of art, beholden to nobody?

And what if instead of an edgy street artist, Endive was just some schmuck with a stack of papers looking to make a buck? How much of this is context? Does being a successful and renowned artist make you more likely to get a free pass on this copyright thing?

And look, I have no definitive opinion either way, other than the fact that I am Rupert Endive's exclusive agent and representative. I'm just throwing questions out there.