It's a memetic disease akin to religion how many person-years of time have been wasted trying to find a use for blockchain lock-in.
No.
Of course it’s still word against word unless the camera itself implements the signing protocol.
Probably want multiple servers from multiple countries, to ensure both redundancy and trust. After all, the requests are cheap and small enough.
As GP said, you are trying to answer a question: "How do I apply blockchain here". This is never a right question, you should instead be asking: "which technology will allow to solve this problem in the most optimal way according to users".