Hmm, video evidence may be trustworthy - eg. video from a CCTV system. Perhaps it could be written onto some write-once, tamper resistant format? Not sure how that would look.
I suppose one place to start thinking about this would be photos. Are photos admissible evidence or do courts only allow negatives? Photos have been modified for a very long time. This is probably the most famous example: https://amp.businessinsider.com/images/52af668569bedd3b2643d...
But yes, I am far more worried about how much more effective fake news will be once they start coming with actual videos.
