Adobe Tackles Photo Forgeries

UnanimousCoward writes: Wired has an article about Adobe working on a way to detect photograph forgeries. FTFA:

In a speech in Tel Aviv in December and a blog entry, Reuters CEO Tom Glocer said his company is working with Adobe and Canon to create an "audit trail" that would reveal changes made to an image. Neither Reuters nor Canon would provide details on the plan.

Isn't it fairly simple? It seems to me that a combination camera/photographer digital signature would solve this problem easily. News agencies would pay for this custom-camera technology (since the public won't), and any photograph submitted without the digital signature would be captioned as such. I'm not sure where Adobe comes into the picture since it could just be general digital signature software that verifies the photo...