Everyone needs to realize that Corbis is not being overly litigious or singling out FR. Protecting the rights of their photographer's images is what Corbis does. This was a very high profile abuse of their copyright. They really have no choice but to pursue it. If for nothing else, to show the photographers in the stock photo world that they aggressively defend their copyrights.
And I am sure they came to FR first because several of the news articles about this image stated that this is where the image originated from. I would bet that most other sites that Corbis is aware of will be getting a letter from a lawyer.
check the disclaimer at another site that posted the pic:
http://www.commondreams.org/headlines04/0220-12.htm
Their disclaimer:
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"We believe this constitutes a 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law.
In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit to those who have expressed a prior interest in receiving the included information for research and educational purposes...
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"Fair use" (should) apply at non-profit discussion websites, such as FR... :)