“If true, there is a photographic record of every ballot that was delivered via US mail.”
A photographic record of every envelope but not the contents. Any fraudulent ballots would likely be contained in an envelope with a phony return address if they used USPS at all.
Butt.
They can individually counted and totaled by ZIP+4 location.
If they took a picture of the envelopes, then that would include the outside code, which could be used to identify the voter. And then the voter name could be compared to the signature on the outside envelope (if there is one - requirements vary by state) to see if there’s a match.