Leslie James Pickering noticed something odd in his mail last September: a handwritten card, apparently delivered by mistake, with instructions for postal workers to pay special attention to the letters and packages sent to his home. Show all mail to supv" - supervisor - "for copying prior to going out on the street," read the card. It included Mr. Pickering's name, address and the type of mail that needed to be monitored. The word "confidential" was highlighted in green. "It was a bit of a shock to see it," said Mr. Pickering, who with his wife owns a small bookstore in Buffalo. More than a decade ago, he was a spokesman for the Earth Liberation Front, a radical environmental group labeled eco-terrorists by the Federal Bureau of Investigation. As the world focuses on the high-tech spying of the National Security Agency, the misplaced card offers a rare glimpse inside the seemingly low-tech but prevalent snooping of the United States Postal Service. 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. The Mail Isolation Control and Tracking program was created after the anthrax attacks in late 2001. It enables the Postal Service to retrace the path of mail at the request of law enforcement. No one disputes that it is sweeping.