An old photograph that was purchased for $2 from a junk shop in Fresno, Calif. in 2010 appears to be an authentic photograph of the legendary outlaw, Billy the Kid, according to Fox NewsThe tintype was said to have been taken a month after the end of the Lincoln County War. It shows Billy the Kid and some members of The Regulators, the outlaw's famous gang, playing croquet.

Kagin's, a company that specializes in rare coins, currency and Western Americana, now holds the five-inch photo. "When we first saw the photograph, we were understandably skeptical - an original Billy the Kid photo is the Holy Grail of Western Americana," Kagin's senior numismatist David McCarthy said in a press release.

Billy the Kid's authenticated tintype is appraised and insured at $5 million, and there are "a couple of people who are interested right now," McCathy told Fox News.

The newly discovered tintype is the the second known photograph of the gunman - the first one being a portrait taken in 1880 depicting him with a Colt revolver and an 1873 Winchester carbine rifle. The first photograph was bought by businessman William Koch in 2011 for $2.3 million.

McCathy said the second photograph was authenticated through facial recognition software that identified four people who were with Billy the Kid. Entries in an old diary helped the company to determine the location of the photo, which turned out to have been taken in the summer of 1878 on the New Mexico ranch of John Tunstall, a former employer of the outlaw, according to McCathy.

"The historical importance of a photograph of Billy the Kid alongside known members of his gang and prominent Lincoln County citizens is incalculable - this is perhaps the single most compelling piece of Western Americana that we have ever seen," Donald Kagin, president of Kagin's, said in the press release.

However, not everyone is convinced of the authenticity of the photo. Daniel Kosharek, photo curator at the Palace of the Governors Photo Archives, said the people in the tintype are too small to be recognized, and the scene did not look like it was taken in New Mexico or Lincoln.

"How this particular one has gained so much traction is beyond me," he told Santa Fe New Mexican. "As you know, this is a rather constantly arising issue which I believe is driven primarily by the sales potential of such a likeness."

The photo will be featured in a two-hour documentary that will air on Sunday, Oct. 18, on National Geographic Channel.