A MAC is symmetric and can thus only be verified by you or somebody who you trust to not misuse or leak the key. Regular digital signatures is what's needed here

You can still use such a signing circuit but treat it as an attestation by the camera's owner, not as independent proof of authenticity.

I think you are misunderstanding things or don’t know shit about cryptography. Why the fuck are y even talking about publicly unlockable encryption, this is a use case for verification like a MAC signature, not any kind of encryption.

Calm down. I was just dumbing down public key cryptography for you

The actual answer is just replace the sensor input to the same encryption circuits

This will not work. The encryption circuit has to be right inside the CCD, otherwise it will be bypassed just like TPM before 2.0 - by tampering with unencrypted connection in between the sensor and the encryption chip.

For your scheme to work, personal ownership rights would have to be severely hampered.

You still don't understand. It does not hamper with ownership rights or right to repair and you are free to not even use that at all. All this achieves is basically camera manufacturers signing every frame with "Yep, this was filmed with one of our cameras". You are free to view and even edit the footage as long as you don't care about this signature. It might not be useful for, say, a movie, but when looking for original, uncut and unedited footage, like, for example, a news report, this'll be a godsend.