(CNN)There are only 100 “Inverted Jenny” stamps in existence. So when one goes on sale, it’s a big deal.
The stamps are known for the printing error that created them. On the stamps is an image of the first plane used for airmail: The Curtiss Jenny. It’s an image that’s on thousands of stamps printed at the time. But on the Inverted Jennys, the image was accidentally — you guessed it — printed upside down.