monitoring of snail mail

"Mr. Pickering was targeted by a longtime surveillance system called mail covers, a forerunner of a vastly more expansive effort, the Mail Isolation Control and Tracking program, in which Postal Service computers photograph the exterior of every piece of paper mail that is processed in the United States — about 160 billion pieces last year. It is not known how long the government saves the images. Together, the two programs show that postal mail is subject to the same kind of scrutiny that the National Security Agency has given to telephone calls and e-mail."