First Edition Artist Proofs
Magic the Gathering is the world's first collectible trading card game. These artist proofs are one of the types of cards sought after by those who collect them.
Sometimes referred to as Beta/Collector's Edition or 'square cornered' proofs, these were provided by Wizards of the Coast to the artists as a means of providing color examples of the artist's work without the artist having to buy and open a bunch of booster packs/product. In most cases, the number of artist proofs in existence is limited to a mere 50 in the world. The front sides look identical to any other Magic card, however the back sides were not printed, but left blank. Since the only initial source for artist proofs is directly from the artist who's artwork is featured on the card, it has become common for collectors to commission artwork on the blank backs when purchasing an artist proof from an artist. The custom artwork on the blank backs both increases the artist proofs value and also serves to authenticate it's source.