The next time you address an envelope, make sure to use your best penmanship — it’s being photographed.

The Postal Service takes pictures of the exterior of every piece of mail processed in the United States — 160 billion last year — and keeps them on hand for up to a month.

In an interview with The Associated Press, Postmaster General Patrick Donahoe said the photos of mail pieces are used primarily for the sorting process, but they are available for law enforcement, if requested.

Many Lowcountry residents said they are not worried about the photographs because they have nothing to hide and the photos are only of the outside of a piece of mail.

“It’s good for security,” said Mount Pleasant resident Eileen Kolb, who went to the Post Office on East Bay St. Friday with her granddaughter to mail a package.

The photos have in fact been used recently for security purposes, specifically involving ricin-laced letters sent to President Barack Obama and New York Mayor Michael Bloomberg.

“We don’t snoop on customers,” said Donahoe, adding that there’s no big database of the images because they are kept on nearly 200 machines at processing facilities across the country. Each machine retains only the images of the mail it processes.

“It doesn’t bother me. They already know where I live,” said Charleston resident Steve Hayden with a laugh.

Neither Hayden nor Kolb knew of the practice before this week, but they weren’t surprised.

The images are generally stored for between a week and 30 days and then disposed of, Donahoe said. Keeping the images for those periods may be necessary to ensure delivery accuracy, for forwarding mail or making sure that the proper postage was paid, he said.

The automated mail-tracking program was created after the deadly anthrax attacks in 2001 so the Postal Service could more easily track hazardous substances and keep people safe, Donahoe said.

“We’ve got a process in place that pretty much outlines, in any specific facility, the path that mail goes through,” he said. “So if anything ever happens, God forbid, we would be able very quickly to track back to see what building it was in, what machines it was on, that type of thing. That’s the intent of the whole program,” he said.

The Associated Press contributed to this report. Reach Jade McDuffie at 937-5560 or jmcduffie@postandcourier.com.