A rare coin dealer in California has concluded that a grainy image of legendary gunman Billy the Kid playing croquet is the real thing and could be worth as much as $5 million.

That is not bad for a photo purchased by Randy Guijarro of Freemont, Calif. for $2 as a part of a miscellaneous lot at a Fresno junk shop in 2010, according to Kagin's. The company is negotiating a private sale of the photo.

"We have a couple of people who are interested right now," Kagin’s senior numismatist David McCarthy told FoxNews.com said.

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The 4x5-inch tintype – which depicts Billy the Kid and several members of his gang, The Regulators, relaxing in the summer of 1878 - will be the subject of a two-hour documentary airing Sunday on the National Geographic Channel.

Taken just one month after the tumultuous Lincoln County War came to an end, it offers a rare window into the lives of these gunmen. Rather than a threatening outlaw, Billy the Kid seems to be enjoying some downtime following what Kagin’s said was a wedding.

The only other known photograph of Billy the Kid is a portrait of the outlaw taken in Fort Sumner, NM in 1880. It sold for $2.3 million to Palm Beach, Fla., businessman William Koch in 2011 at Brian Lebel’s Annual Old West Show and Auction in Denver. In that photo, Billy is packing a Colt revolver and trademark 1873 Winchester carbine rifle.

When they first got hold of the latest image, McCarthy said they weren’t sure it was authentic adding that "if you do an Internet search, there will be 20 people who have a photo of some guy that looks like Billy the Kid."

“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.

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“We had to be certain that we could answer and verify where, when, how and why this photograph was taken. Simple resemblance is not enough in a case like this - a team of experts had to be assembled to address each and every detail in the photo to insure that nothing was out of place,” he continued. “After more than a year of methodical study including my own inspection of the site, there is now overwhelming evidence of the image’s authenticity.”

McCarthy said experts began believing the tintype was real after they were able to determine that four people in the photo - using facial recognition software - were those who spent time with Billy the Kid. Then, they began looking for events in which they were all together around that time.

They stumbled upon a diary of Sally Chisum, in which she described a cattle drive featuring all the players in the photo as well as a wedding that took place between Charlie Bowdre (seated on the horse in the photo) and his wife Manuella.

The cattle drive helped researchers narrow the location of the photo to New Mexico and the former ranch of one of Billy the Kid's employers, John Tunstall. But to confirm the site of the photo, McCarthy actually flew out to the site near Roswell and examined a building that turned out to have been built "over and around" a structure that was actually in the photo.

“I was standing at an angle from the building and I could see the texture of the stucco on the front of the building,” McCarthy said, adding they were tipped off by an investigator who saw what the thought was a building from the photo on ranch. “You could see the vertical wooden supports through the stucco and I

looked at the picture and they were in the exactly the same place. I was amazed. That clinched it.”

Kevin Costner will narrate and produce the two-hour documentary for National Geographic Channel, covering Western Americana enthusiast Randy Guijarro’ s odyssey to authenticate this unique photograph. The documentary will also feature extensive interviews with a variety of experts in digital facial

recognition, antique photography, geographic positioning, and vintage croquet sets.

“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,” Kagin's President Donald Kagin said, in the press release.