I suspect in the not too distant future we'll need a way to produce provably true videos. I'm thinking something like the subject, a politician giving a press conference for example, carries something that emits a signal that the cameras encode into the video in a way that any alterations could be detected, something like a cryptographic signature. I don't really know enough about cryptography time be sure how / if it would work.
I've been trying to think of a way to popularize digital signatures so when a video is purporting to be a CSPAN clip, you could check that the authorship is really CSPAN, but this always relies on trusting your sources, and who's to say CSPAN won't get hacked? Maybe they already were. [1]
I like your idea, it reminds me of something I stumbled upon reading about the 60Hz hum of AC electricity.
"...this side effect has resulted in its use as a forensic tool. When a recording is made that captures audio near an AC appliance or socket, the hum is also incidentally recorded. The peaks of the hum repeat every AC cycle (every 20 ms for 50 Hz AC, or every 16.67 ms for 60 Hz AC). Any edit of the audio that is not a multiplication of the time between the peaks will distort the regularity, introducing a phase shift. A continuous wavelet transform analysis will show discontinuities that may tell if the audio has been cut."
I believe you already know this, hence the "probably" part, but such analog media can easily be produced from (modified) digital media, thus no credibility.
news agencies could just use an encrypted video stream, since only they have the private key you'd know it came from them and could be trusted as from them.
