In the USA they already take passport photos. Being able to receive mail addressed to a name is the closest thing to a national ID the USA has. They're already depended on for identity verification quite a lot.

You can receive mail to any name at your address.

I didn't say it was a good national ID system, I said it's the closest thing the US has to one.

Some post offices in the US also function as a so called notary public. Basically, they can verify your identity and attest that it's you who sent/did something.

This is used quite often for important things that don't have offices themselves.