Even easier with video: Hash each frame in a way that's dependent on the previous frame. A hashchain, if you will.
Totally impossible with text, of course. AI text can be, in theory, genuinely undetectable.
No. This can be only solved by having "integrity", something very few journalists have.
Stable Diffusion has been kicking around in the wild for a couple of years now, and probably a million people are running it. You can't really criminalize that.
But key generation and storage can be in a hardware module, and tied to a unique device, so it would be quite difficult to hijack -- and, if you did, you'd only get very limited use out of it. So there might be a technological solution. Maybe not a perfect one, but one that's at least plausibly useful.