> The resources needed to forge a signature aren't going to be much different than the resources needed to create a deepfake to begin with.
How? If you have a public/private key pair and then do some kind of multisig process wherein the manufacturer can sign the photo, the OS can sign the photo, and then a user supplied signature could also sign the photo. You're not going to be able to fake 3 cryptographic signatures without 3 private keys. It would be extremely difficult to fake all of that. It would take a concerted, concentrated effort and would be extremely rare in practice. It would certainly improve the situation.
How? If you have a public/private key pair and then do some kind of multisig process wherein the manufacturer can sign the photo, the OS can sign the photo, and then a user supplied signature could also sign the photo. You're not going to be able to fake 3 cryptographic signatures without 3 private keys. It would be extremely difficult to fake all of that. It would take a concerted, concentrated effort and would be extremely rare in practice. It would certainly improve the situation.