No need to think that far. Just calculate the hash of the video file stored on camera (or segments of it during e.g. live stream) and authenticate this using a private key stored in a secure element on the camera. Do you trust this secure element enough (see the breach of Intel’s CPU Private Keys via SpecEx, maybe you can do so by loading a custom firmware as well?).

Assume the secure element is in fact secure, the issue then, as with any public/private key scheme, lies with establishing trust of the keypair. Do you trust the manufacturer that he will not be breached?

And more pressing even; How do you prevent someone modifying their internal camera video stream such that they may send any data to the authentication chip/mechanism?

And if all this is implemented, it can be done even more low level - just direct the camera e.g. to your screen (I assume solutions would then crop up to increase the fidelity of such a solution).

I am not saying such a solution would not provide ANY benefits, I am just pointing out that these issues prevent it from becoming a silver bullet.