Obscuring faces for privacy, cropping would no longer work. And even minor touchups like lighting would be of questionable value since you're expecting users not to look at the edited photo or at least to primarily look at the edited photo next to the original.
I suspect in practice that doing edits on top of a signed photo would be basically the same as not having editing capability at all; and even that's assuming users would compare the edited and non-edited versions at all, which is not a safe assumption in my mind given how hard it is to even get people to click into a full article past the headline.
You could also handle cropping and omissions by having the original device sign the picture as a grid of individual tiles. Then you could omit some and still prove that the others are original.
> You could also handle cropping and omissions by having the original device sign the picture as a grid of individual tiles.
is a pretty good idea, I like that quite a lot. Not saying it means I'm on board with signatures overall (I mean, we're still in agreement that this would require locking down devices to at least some degree) but I do think that's an elegant solution for the cropping/censoring part of it.
Well of course they would. Otherwise what are you even trying to attest? Otherwise someone could take an image from a camera, replace literally every pixel with whatever they want and then claim it's the same image.