I believe Corbis has no leg to stand on here. They cannot hold Free Republic responsible for another hosting site holding copies of their copyrighted images. In such an instance, any lawyer will tell you that it's the site that
hosts the image that is in violation of copyright and should be given notice, not anyone who links to it.
For any attorney to suggest otherwise is to argue that any Free Republic link to a pro-Kerry URL is an endorsement of Kerry. It flies in the face of logic and common sense.
I know that your resources are not infinite, but I seriously think you should take this matter to a copyright lawyer. Unless I am grossly misunderstanding copyright law, they will agree with my assessment of this matter.
You weren't here when the LA Times/Wash Post sued Free Republic (and therefore JimRob). Anyway, we all thought we had a great case. It was "Fair Use" all the way. (I personally still think it does.) FReeper lawyers gave pro bono time to represent us. We still lost, in the eyes of the Clinton-appointed liberal judge. The judgement sucked. It was appealed, IIRC, and we still lost. Jim doesn't have the funds to take it all the way to the Supremes, so he settled.
Anyway, what is JimRob to do? The LA Times/Wash Post settlement could have cost him a fortune that he doesn't have. JimRob doesn't need the heartache of that all over again.