> how to use the DMV's public key to check whether a California ID is real.

That's not what the signature guarantees, though. It says the combination of textual information on the card is *someone's* valid driver's license. The signature doesn't even cover the photo! It just limits the forgeries to using identities of real people.

Compare to https://en.wikipedia.org/wiki/Biometric_passport that actually contains a digital photo, with a signature.