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.
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.