Using trusted computing and related technologies it should be entirely feasible to build tamper-proof cameras that produce provably-real photos, including trusted timestamp. It should be a small step for example for Apple to add such a feature to their future iPhones, given the layers of security they already have in their hardware.
you are talking about secure infrastructure, but the image itself can be still faked. And no such infrastructure is safe, in the end, when given entirely to the end user (modify camera sensor, transfer signed image to an intact device).
