$1,631,700 Possibly the most well-known stamp for collectors. The Inverted Jenny, also known as the Upside Down Jenny, is a 24-cent United States postage stamp issued on May 10, 1918. Its most distinctive feature is that the image of the Curtiss JN-4 airplane in the center of the design is printed upside-down. This error occurred during the stamp’s production, making it one of the most famous and sought-after errors in American philately. Only one pane of 100 inverted stamps was ever found, adding to its rarity. (Getty Images)