The United Kingdom is honoring its working dogs with a new series of stamps illustrating the vital roles they perform.

The issue commemorates two events -- 2008 is both the Year of the Assistance Dog and the 100th anniversary of police dogs in Britain.

The first-class stamp honors assistance dogs who are trained to raise the alarm when an owner is in distress. Others honor mountain rescue dogs, police dogs, customs dogs, guide dogs and sheep-herding dogs like the Border Collie.

The stamps are based on the work of animal photographer Tim Flach.

"It's easy to forget that there's a 'secret army' of thousands of hardworking dogs who make a real difference to many lives," said Julietta Edgar, head of special stamps for Royal Mail. "I hope that this issue will help raise the profile of their important work as customers see the dogs on millions of letters and parcels every day."

(Photo courtesy of Royal Mail)