Several things, the photos, real, fake, and sources for the composite are prohibited by their creators from appearing ON FR.
Which is odd because the only OWNER of the fake is the guy who created it, not the guy who’s photos he used. In the absence of a court order, the ownership of the image does not transfer.
The Lefties at Snopes got a notice from Corbis which made them revise their copyright information but I doubt they PAY Corbis for the image that they host on their own servers. And I know they aren’t paying the creator of the hoaxed image (which can be found here on Snopes where they kept the topic alive).
http://www.snopes.com/photos/politics/kerry2.asp
The creator of the fake composite would have to come forward and assert copyright. And then prove it, no mean feat for an image that's been circulated around the world anonymously.
He'd be on the hook for infringing on the original photos -- despite your assertion, the original photographers do have a copyright interest in derivative works, and could claim substantial damages if they can successfully argue that the fake harmed their reputation or the salability of their genuine photos.
The Lefties at Snopes got a notice from Corbis which made them revise their copyright information but I doubt they PAY Corbis for the image that they host on their own servers.
They might have paid Corbis; I don't know, and neither do you. They also would have a pretty credible fair use claim, because the photo itself is the topic of a legitimate news story.