When Randy Guijarro bought the item, he had no idea that the old photograph was in fact an image of the Wild West icon. The photograph was taken in 1878, and has been confirmed by San Franciso's coins specialist Kagin's that it is indeed of Billy the Kid.

The only other known photo of Billy the Kid was bought in 2011 at Brian Level's Old Western Auction, Denver, for an incredible $2.3 million by billionaire and American West collector Bill Koch. Guijarro's photo of Billy playing croquet has been insured for $5 million.

billy-the-kid-croquet-1-1024x820 Billy the Kid in 1878.
Image via Kagin's

Billy the Kid was born Henry McCarty in New York. He made for the west and became one of history's most infamous frontier outlaws.

Kagin's David McCarthy said in an interview with the Guardian: "An original Billy the Kid photo is the holy grail of Western Americana."

"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."