In the same way a suspect may be declared guilty when e.g. there were reasonable expectation to double check a published image, a possibility to do it, obvious benefits from spreading fakes. Even if that image is genuinely looking convincing.
Probably, eventually somebody will try to use it to silence real whistleblowing. And it's unclear how this will work at all with expected advancements of generation capabilities. But I believe there's a public demand for such law.
I expect pretense of uncertainty to be used to get around: "we got this video from unknown source and we are not sure if it's AI-generated, but look like how this politician f*cks a pig"