I feel the trouble with this is two-fold: It's not enough that the photograph is signed and has metadata. Someone has to interpret that metadata to decide auth

I feel the trouble with this is two-fold: It's not enough that the photograph is signed and has metadata. Someone has to interpret that metadata to decide authentic versus not. One can have an "authentic" photo of a rear projection screen. It wouldn't be appropriate to have an "authentic" checkmark next to this photo if it claims to not be a photo of a rear projection screen. The context matters to authenticity. Secondly, the existence of such "authentic" photos will be used to call all non-authenticated photos into doubt. So it doesn't even really solve any problem, but creates new problems.