I believe what HN User gambler was getting at is a world far more insidious. One where no one cares whether or not file B is fake. No one cares whether transcoded file C is fake. He's talking about a world where the power elites have effectively set themselves up as the only source of cryptographically secure and verified image feeds.
ie - A world where so much fake image data has flooded into the zeitgeist that people only believe the feeds that are announced to be "real" by their cryptographically secure devices. They can play the fake video, even play video that may not be fake, but was not cryptographically validated. Their devices will just be flashing a huge warning sign right next to each such image feed. (Or even worse, it will only flash a "real" sign next to the image feeds it and the central have concerted to cryptographically validate.) It'd be kind of like the huge warning dialogs that always popped up at a certain point when people went somewhere with an ActiveX plugin in the page. After a while, it wasn't just ActiveX, it was everything. People just got conditioned to believing that every plugin, no matter the source, was horribly bad for them. (Every plugin probably was, but that's a separate issue.)
Only this time, the powers that be will be the only ones capable of delivering data that is guaranteed to be pure. Everything else will be either, not validated by their cryptography standard. Transcoded, (and consequently the masses will dismiss it out of hand). Or out and out fake, (which, yes, the masses should dismiss out of hand. I get that).
But I'm just saying that people should think a little further ahead here when they are trying to solve this problem. If we want to use cryptography to solve this problem, that's perfectly reasonable. (And yes, it would work. It would work only too well, and that's the entire problem.) I'm only saying that we should do what we can to make sure that cryptographically validated image feeds are not uniquely identifiable, for instance. Because when you go down this road you need to realize that with hardware cryptography, the hardware makers and those with power over them become de facto arbiters. And they can potentially use distribution to control the masses. Because they have the only pure sources. They could potentially even use attribution to control the masses. (You sure you want to video tape that police beating and mail it to the media "anonymously" with one of these devices?)
I'm just saying. Stop and think it through a bit.
And having a plan based on, "Oh... We're smart enough to get around it!" Is a very foolish plan for two reasons. First, because we won't be able to get around it, and second because it's the same as having no plan at all.