If you're unsure as to whether or not you need a Certificate Of Authenticity, consider this passage from
Legal Guide For The Visual Artist

A little history...

In 1971 California became the first state to enact legislation regulating the sale of fine prints. The statute was extensively amended in 1982, including extending it's coverage to multiples other than fine prints The statute starts by defining "fine-art, multiple, fine print, master, artist, signed, unsigned, art dealer, limited edition, proofs, written instrument and person". A fine-art multiple is defined as "... any fine print, photograph (positive or negative), sculpture cast, collage or similar art object produced in more than one copy".

The statute limits it's application to any sale of a multiple for a price of $100.00 or more, exclusive of the cost of framing. When an art dealer sells such a multiple in California, a written instrument must be provided to the purchaser with information regarding the multiple. An artist, though not considered an art dealer, must also provide this information whether selling or consigning a multiple. If the artist does this, he or she will not be liable to the final purchaser of the multiple. This information includes the name of the artist, whether the artist signed the multiple, a description of the process by which the multiple was produced, whether the artist was deceased at the time the master image was created or the multiple was produced, whether there have been prior editions and in what quantity, the date of production, the total size of a limited edition (including how many multiples are signed, unsigned, numbered or unnumbered and whether proofs exist) and whether the master has been canceled after the current edition.

The penalties for violating the law may include refunding the cost of the multiple plus interest, and damages of triple cost of the multiple if the violation is willful. The California law was amended in 1988 to require a certificate of authenticity when a multiple is sold by an art dealer into or from California. A certificate of authenticity is defined as "a written or printed description of the multiple which is to be sold, exchanged or consigned by an art dealer". The law requires every certificate to contain the following statement: "This is to certify that all information and statements contained herein are true and correct."

Reprinted here with permission from the author.

To purchase the the latest edition click here...

Legal Guide for the Visual Artist, 5th edition, Tad Crawford, Allworth Press

Here is a sample of the certificate of authenticity I provide at your request.