The embarrassing slip-up follows the introduction in February of an Internet service allowing Germans to handpick images to be printed on stamps that are then sent to them, spokesman Dirk Klasen said.
Normally the choices are thoroughly vetted so that pornographic or other offensive images do not enter circulation.
"But when it came to the one with Hess, there was a problem," Klasen said.
Hess parachuted into Britain in 1941 and was kept prisoner for the remainder of World War II before being sentenced to life imprisonment at the Nuremberg trials in 1946.
He committed suicide at Spandau prison in Berlin in 1987 aged 93.