A certificate of authenticity is used to verify that a product is what it is claimed to be. This can be important when determining the value of a product, or when verifying that a product is genuine. Certificates of authenticity are used in many different industries, but they are especially important in the art world. When buying or selling a piece of art, a certificate of authenticity can be used to verify that the piece is genuine and has not been altered in any way. Think of a certificate of authenticity as a passport or piece of ID for your art.