A composite solution: The camera's chip produces two signatures for each image: one fairly resistant to cropping, color correction, rotation, etc. and resistant

A composite solution: The camera's chip produces two signatures for each image: one fairly resistant to cropping, color correction, rotation, etc. and resistant to forging; and a second, pixel-perfect one. The photographer that wishes to be able to claim authenticity uploads the photos to the camera makers website, which verfifies the authenticity of both signatures and publishes both in a secure database indexed by the "editable" signature (and his name, if he wants proof of authorship). Now, if the author wants to claim authenticity or ownership of a picture, he just has to present the original picture so that people can attest it is not significantly modified and/or he is indeed the author. Of course, reading the private keys on the chip has to be very hard.