Chain of custody implies you have some impartial authority who was actually there at the time to authenticate the recording. But then you would already have an impartial eyewitness. That doesn't work the other 99% of the time when the two parties to the case each tell a different story and one of them is offering evidence they have in their possession. The chain of custody then contains someone partial to the case and untrustworthy.
> Yes, if a state actor wants to create evidence to frame you, and they didn't care about cost or returns, they could do so. But they could always do so. The fact is most of us are never going to get framed by a nation state.
This is a major problem for elections. Nation states absolutely will doctor video of adversarial political candidates and for other propaganda purposes.
> The notion that you're either secure against all possible attacks or nothing is absurd.
But that's how signatures work. You're trusting every device in the world to sign the output of its camera. If the attacker can compromise any device, they can produce signed forgeries.