A camera could be hacked with unrestricted physical access, but that doesn't make the suggestion unsound, it only requires there be a process for revoking trust

A camera could be hacked with unrestricted physical access, but that doesn't make the suggestion unsound, it only requires there be a process for revoking trust in specific signing keys. This is already part of C2PA. And the value of the signature is also going to vary by who claims it. Improbable photos signed by a random camera body sold to an anonymous consumer should be treated with more suspicion than one a newswire agency publicly claims, for instance.