Try one of the most famous printing mistakes in U.S. postal history: A 1918 airmail stamp with the plane printed upside down! Nicknamed the “Inverted Jenny” (the stamp pictures a Curtiss “Jenny” airplane), this stamp is valued at $400,000, and a block of four is valued at $3 million! (Original price: 96 cents.) An 1847 10-cent George Washington stamp in mint condition is worth about $27,500!
