A newly-surfaced photo of legendary outlaw Billy the Kid is being called "the Holy Grail of Western Americana."

The 4-by-5 inch tintype was bought for $2 by collector Randy Guijarro at a Fresno, Calif., junk shop in 2010. Experts now say it could be worth $5 million.

The photo shows Billy, whose real name was Henry McCarty, playing croquet with his posse, the Lincoln County Regulators, outside of a cabin in the summer of 1878, according to Western experts Kagin's.

There's only one other known snap of the Kid. It went for $2.3 million in 2010.

National Geographic will air a special tracing the photo's history on Oct. 18.