> cryptographic signatures in cameras strike me as a useful application of blockchain technology
As always with "blockchain", you have to ask the question, "couldn't this be done with non-blockchain technologies, at a fraction of the energy cost?"
There are as far as I can see two things which could be authenticated: "was this photo taken by a physical camera", and "was this photo taken at a particular moment in time". For the first, the camera could sign the RAW file, and append a certificate signed by the camera's manufacturer; AFAIK, cameras which do that already exist. For the second, cryptographic timestamp services are older than blockchain (RFC 3161, see https://en.wikipedia.org/wiki/Trusted_timestamping for alternatives), and IIRC were used in Windows to timestamp signed binaries, so that they would keep working even after the key used to sign them expired (as long as the signature was timestamped prior to that expiration).
As always with "blockchain", you have to ask the question, "couldn't this be done with non-blockchain technologies, at a fraction of the energy cost?"
There are as far as I can see two things which could be authenticated: "was this photo taken by a physical camera", and "was this photo taken at a particular moment in time". For the first, the camera could sign the RAW file, and append a certificate signed by the camera's manufacturer; AFAIK, cameras which do that already exist. For the second, cryptographic timestamp services are older than blockchain (RFC 3161, see https://en.wikipedia.org/wiki/Trusted_timestamping for alternatives), and IIRC were used in Windows to timestamp signed binaries, so that they would keep working even after the key used to sign them expired (as long as the signature was timestamped prior to that expiration).