Passports have digitally signed certificates in them, readable by any device with an NFC radio. It's easy enough to extract that data with a mobile app, and now you have an unforgeable file that can be hashed. Of course whether users will bother to sign up for something like a social network if they have to go rummage around and find a passport, install a mobile app etc, I don't know. But it's technically possible and I've proposed such a scheme years ago. For bonus points do the hashing inside a secure enclave so the ePassport data is never upload to a remote server in the clear.