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For alibi, in the future it would probably be a good idea to have a 24/7 personal body camera which timestamps the video using the blockchain or something.

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A perfect way to counter misinformation from foreign and/or domestic hostile powers. Sign everyone up. Whoever refuses gets a hit to their social credit rating.

Would have to be self-contained; otherwise, the video could always be edited...

Perhaps camera sensors could digitally sign their output using an invisable watermark? It's been an idea I've had since deep fakes became a thing.

Doesn't really solve the problem, there are many ways of bypassing that, from having a small screen in front of the lens playing fake video, to hacking the firmware.

Obtaining the hash value of a video, then embedding that hash value into a secure block chain is one approach that gives evidence that a specific video (or any other document) existed before some point in time.

See, for example:

https://petertodd.org/2016/opentimestamps-announcement

Editing the video after the fact changes its hash value, thereby invalidating the timestamp on the altered video.

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