Comment Better Solution (Score 1) 28
Actually, it occurs to me that there is a technological solution to this problem. Simply have camera device makers sign their output using some kind of secure hardware key so the receiver can verify that the video was the input as seen by the camera on a X laptop or whatever. Of course, you still need to guard against attacks that stick a screen in front of a camera but that's doable if the camera has any focusing information or uses IR lines to reconstruct 3d information.
I'm sure there will be all sorts of clever ways you can sign the image stream that will be robust to a degree of encoding or other changes. Simplest option video calls display the signed still picture and maybe youtube videos display some uncompressed frame every so often or check that it matches. But I suspect you can do something cleverer than that.
But algorithmic detection is unlikely to be the answer unless it's an interactive situation where the detector can issue queries.