The central problem seems to be that the people who are in a position to benefit from claiming something is fake that's actually real are the same ones you have to trust to determine whether it's fake, since the viewer can't determine that (even if they provide a black-box program that supposedly checks this, you can't know what it really does so the same trust problem exists). Maybe this would be useful for a while in an organization to be sure employees aren't using editing and tools on video.