Finding an original copy on a go-pro would likely be pretty compelling evidence but this (and the more scary politically centered questions like this) are why I wish we had a way to build a durable chain of custody into these technologies. It is infeasible from everything I've seen but it would be a big win for society.
We'd probably hit a lot of that with SSL if it wasn't so unimportant from a political perspective[1]... but if the thing we were trying to secure is going to boost or damage some prominent politician directly then the level of pressure is going to be on a whole different scale.
1. And we might still have that corruption of SSL when it comes to targeted phishing attacks.
I don't think that's true. Only for someone who wanted to prove authenticity to grab the signature. No private keys would be exposed (except those which were hacked.)
If Netflix and Amazon can't keep their 4k HDR webrips from being leaked (supposedly via extracted licenses from Nvidia Shields), I have no idea how we'd expect all camera manufacturers to do it. Maybe iPhones and flagship Apple devices, but even then we'd find vulns in older devices over time.