People predicted that Photoshop was the end of truth, that journalism could no longer be trusted, that photographic evidence at criminal trials would be inadmissible.

None of that actually happened because people learned to be skeptical, and to care about who took the photo, the chain of custody, and the controls to prevent digital alteration.

Maybe we need something similar but more rigorous for video. The camera itself could encode a PKI signature in every frame of the original. If subsequent edits preserve frames as is, then the viewer could determine how many frames were cut or duplicated.

If subsequent edits crop, recolor or otherwise alter the frames, that editor could encode its own digital signature so the viewer could judge how much to trust their edits.

I don't completely agree, good quality photo editing, even in this day and age, is not that mainstream. You need a decent amount of skill to edit a good quality picture in a way that won't look obviously fake. Pre-digital-photography it was only possible for skilled people with a significant amount of resources (like the Soviet government, no doubt).

Besides it's one thing to edit a still image and a whole other to forge a long video, complete with audio. Look at those movies these past few years using 3D models to insert younger versions of actors (Terminator and Star Wars come to mind). They must have invested millions into it, they have very talented artists and it's pretty good but it's still quite easy to spot the fakeness of it.

And why dont I hack the key out of the encryption chip and make as many shops as I like?

And why doesn't the government keep track of the cameras and security keys so they can trace back any images they do not approve of?