Man bought old photo for $2 and learned it was worth $5,000,000 after experts discovered who is in the picture

A photo dubbed 'the holy grail of Western Americana' was discovered by a man in an antiques shop by chance.

Collector Randy Guijarro happened across the photograph in question at a store in Fresno, California, and bought it for just $2 in 2010.

The black and white tintype photograph shows a group of people stood outside a barn, some of whom were playing croquet.

Taking the photo home, Randy went on to study it under a microscope and recognized one of the people.

He realized that one of the men playing croquet was Henry McCarty - best known as 1800s outlaw, Billy the Kid.

Randy had the image authenticated by a San Francisco-based Americana company, Kagin’s, which confirmed that it was McCarty in the photo.

He was seen alongside several other members of the Lincoln County Regulators in New Mexico.

It's believed the snap dates back to 1878 - three years before McCarty was killed.

Randy's find is only the second authenticated photograph of the notorious outlaw. The first genuine authenticated photo of Billy the Kid sold for $2.3 million in 2011.

Randy Guijarro purchased this photo for $2 in 2010 (Kagin's Inc.)

With its rarity in mind, it went on to be valued at a whopping $5 million, The Guardian reported in 2015.

When Randy first took the photo in to be authenticated, the experts were understandably skeptical.

"An original Billy the Kid photo is the holy grail of Western Americana," David McCarthy from Kagin’s told The Guardian.

"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 ensure that nothing was out of place."

Further investigations found Billy the Kid to be in the photo (Kagin's Inc.)

Following his historic discovery, Randy urged others to go treasure hunting.

"I hope this prompts others out there to look into trunks and attics because there are so many lost treasures out there," he said.

In regards to what he planned on doing with his newfound wealth, Randy went on: "We could use a new vehicle. We’d really like to look for lost pieces of history be it US or worldwide. We love to be adventurers. The hunt is a really grand thing."

The monumental find and its five-year journey to being authenticated was detailed in a National Geographic documentary narrated by Kevin Costner called Billy the Kid: New Evidence.