[oulipo]

I guess perhaps the easiest would be that each personality has a website where he can sign (using his private key) his appearance in some media at a given time and for a given duration (using the hash of the media, or some QR code embedded in the media)

[latexr]

That doesn’t prove a video is real, only that the person claims it is. The point seems to be be that the one watching could verify by themselves.