The latest book by Bob Schneider "Data and Goliath", says:
"Through a program called Isolation Control and Tracking, the US Postel Service photographs the exterior, front and back, of every piece of mail sent in the US. That's about 160 billion pieces annually."
Apparently, there are 2 programs, one old and one new:
- "Mail Covers Program" is on demand, and records the exterior of all "mails" and "parcels". However, this is on-demand and only applied in the numbers like tens of thousands a year.
- "Mail Isolation Control and Tracking" applies to all letters. (It is not clear if this applies to non-machinable letters or flats, which are hard to automate). Apparently a machine photographs the front and back automatically as a barcode is sprayed automatically onto the letters.
New York Times has a pretty detailed write up about this here: