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.