A new National Geographic documentary chronicles the journey taken to verify the latest image of the Irish-American outlaw.Public Domain/Wikicommons

A lucky $2 junk shop purchase including a photo of infamous Wild West outlaw Billy the Kid and the Regulators gang could now fetch up to $5 million.

In 2010, Randy Guijarro happened across an interesting 4x5 inch tintype picture of a group playing croquet at a Fresno, CA junk shop. He purchased for the tintype for $2 along with two other photographs.

Despite a long battle, Guijarro has now been able to confirm that the bottom-dollar purchase is worth big bucks, being only the second known picture in existence of notorious Billy the Kid in the midst of the iconic Regulators gang.

In a National Geographic special to be aired this weekend, Guijarro details his struggle to prove the item in his possession was worth more than he’d previously imagined, especially after the first known image of The Kid was confirmed in 2011 and sold for $2.3 million. Many chanced their arm at making the same kind of money on the rarity of Billy the Kid’s image following this discovery and were quickly brushed aside by the few accredited with the skill to identify the tintypes as genuine.

Guijarro was among those shot down by the professionals believing he was just another person willing to take a chance or someone who wrongly believed that they had discovered something precious.

READ MORE: Photo shows outlaw Billy the Kid as clean cut and preppy.

Jail and courthouse in Lincoln, New Mexico, where Billy the Kid was tried. Image: Public Domain/WikiCommons.

Jail and courthouse in Lincoln, New Mexico, where Billy the Kid was tried. Image: Public Domain/WikiCommons.

He was determined in his quest, however, and with the help of Jeff Aiello, one of the producers of the National Geographic special, Guijarro tracked down the evidence to prove he was right, traveling to the the now-abandoned building featured in the the back of the image in the process.

Wild West outlaw Billy the Kid was the son of Irish immigrants believed to have been born Henry McCarty in New York City in 1859, although his exact date of birth is unknown. His family soon headed west where he was arrested for the first time at just 16 years of age for stealing clothes in New Mexico.

Not much is known regarding McCarthy’s father, but his mother is said to have been named Catherine McCarthy with debates over whether McCarthy was her maiden or her married name. According to Biography.com his father left when he was young and McCarthy was then orphaned at 15 when his mother died of tuberculosis.

As he descended into criminality, Henry McCarthy fled from town to town earning the moniker Billy the Kid from his short stature and his age, although he also used other aliases such as Henry Antrim and William H. Bonney.

In the 1870s, still only in his teens and early 20s, he became the most notorious member of the Regulators, the bunch of outlaws organized to protect the cattle business of Englishman John Tunstall.

As legend has it, McCarthy killed as many as 21 men, one for every year of his short life, although historians believe the figure may be closer to between six and nine. He is said to have killed for the first time at 17 years of age, although this too could be too high as the exact year he was born is uncertain.

It was the murder of Regulator’s boss Tunstall in February 1878 that started the Lincoln County War as the gang took action to avenge the death of their benefactor. The war came to an end with the Battle of Lincoln on July 17 when the Army intervened and the Regulators either fled or lost their lives.

Billy the Kid was placed on a wanted list in the aftermath of the Lincoln County War with a hefty bounty of $500 on his head. Despite his initial capture and sentence to death by hanging in 1880, The Kid killed two further deputies and managed to escape.

The outlaw was captured soon after and shot in a sting operation by Lincoln County Sheriff Patrick Floyd Garrett, also the grandson of Irish immigrants.

READ MORE: Top ten Irish outlaws and gangsters, from Ned Kelly to Whitey Bulger.

Billy the Kid's grave. Image: Public Domain/WikiCommons.

Billy the Kid's grave. Image: Public Domain/WikiCommons.

In 2011, the first picture of the famous Irish Wild West out-law was confirmed, reaching a staggering price of $2.3 million when put on sale. The picture of The Kid looking smug was taken in 1880 and sold to businessman William Koch. Comparisons between this image and Guijarro’s show striking similarities including the hat perched precariously upon his head for which McCarthy was famous.

When producer Aiello learned of Guijarro’s struggles to confirm the importance of his random junk-shop purchase, he got in contact with the collector to ask if he would be interested in taking part in a self-funded documentary that would chronicle Guijarro’s journey to win verification.

Already aware of the Billy the Kid story, Guijarro had identified others in the group pictured as other members of the Regulators and the pair took the next steps in confirming that the people identified would have been in the Kid’s company at the time the photo was taken.

They finally reached their big breakthrough when Aiello's wife Jill succeeded in tracking down the diary of one of the woman believed to be pictured, Sally Chisum, and identified a time when all the members also believed to be photo would all have been together.

It is now believed that the photo was taken at a wedding between gang member Charlie Bowdre (seated on a horse to the right of the picture) and his bride Manuella. According to the diary, the pair married around the middle of August to the first week of September 1878 - just weeks after the Lincoln County War ended.

As it became more apparent that Guijarro had a genuine image on his hands, National Geographic voiced their interest in the documentary, appointing as narrator Kevin Costner, who had also expressed his belief in the authenticity of the photo.

The next step in the confirmation process involved facial recognition and volunteer Ken Gibson offered his services to carry out the test. Individuals in the image received scorings in the 70s and 80s, well above the 60 percent point required in a court of law.

Still not providing enough evidence to confirm the image of Billy the Kid was real, the final breakthrough came as the team searched for the exact spot where the photo was taken. After months of searching Google Earth to no avail, they finally decided to explore other options, turning to John Tunstall as a key figure who would further their research.

As the founder and organizer of the Regulators, it was believed that Tunstall may have provided the image’s backdrop.

Traveling to the known location of Tunstall’s ranch, the researchers found the building in the image still standing although with another structure built up around the original. Removing this, the original lumber was still beneath, acting as the final confirmation that this was indeed the first known picture of a group of Regulator members with Billy the Kid fourth from left.

After his long years of research, Guijarro now plans to sell his discovery for a more than acceptable $4,999,998 profit.