This was just announced on the cc-community mailing list:
http://s1.imagestamper.com/login.jsp "Stay copyright-safe Using creative commons images? Prove you have the right with ImageStamper. ImageStamper is a free tool for keeping dated, independently verified copies of license conditions associated with creative commons images. Whether you are a blogger, a PR agency, a freelance photographer or a media production company, ImageStamper will give you peace of mind when it comes to using creative commons images. "
I think we've kinda solved this problem now?
cheers, Brianna