In 2010, Randy Guijarro bought three old photographs he liked at a junk store in Fresno, Calif., for $2, including a 4-by-5-inch "tintype" showing a bunch of men playing croquet near a cabin in 1878. But not just any men—nearly a year of authentication proved that the photo shows Billy the Kid and members of his gang of outlaws, The Regulators, and now the picture (which, the Sacramento Bee notes, actually cost Guijarro only 88 cents) is going to auction and could sell for $5 million, USA Today reports. "When we first saw the photograph, we were understandably skeptical—an original Billy the Kid photo is the Holy Grail of Western Americana," says the senior numismatist at Kagin's, the firm of experts that authenticated the tintype and will negotiate its sale. There's only one other known photo of Billy the Kid, taken in 1880, and that 2-by-3-inch tintype sold for $2.3 million in 2010.
The process of authenticating the newly discovered picture of Billy (real name William Henry McCarty Jr. , though he also used the alias William H. Bonney) will be explored on a National Geographic special Sunday. It all started after Guijarro enlarged the image he'd bought and thought he recognized Billy the Kid and his best friends, Tom O'Folliard and Charlie Bowdre. Sallie Chisum is in the picture, too, ABC30 reports, and Fox News notes that research of her writings revealed the photo was taken after Bowdre's wedding. "We had to be certain that we could answer and verify where, when, how, and why this photograph was taken," the numismatist says. Experts in digital facial recognition, antique photography, geographic positioning, and even vintage croquet sets were brought in and will be featured on the documentary. "It's the holy grail of not just Western photography. It's the holy grail of photography," the executive director of the documentary tells the San Francisco Chronicle. (Read more Billy the Kid stories.)