The only surviving authenticated portrait of the infamous 19th century outlaw sold at an auction on Saturday in Colorado for $2.3 million.
The tintype portrait went to a private collector.
A 15-percent fee was added to the bidding price, making the selling price more than $2.6 million.
Organizers had expected it would fetch between $300,000 and $400,000.
The portrait is believed to have been taken around 1879 in New Mexico. It shows the outlaw dressed in a rumpled hat and layers of clothes, including a bulky sweater. He's standing with one hand resting on a Winchester carbine on his right side and a Colt revolver holstered on his left side.
Tintypes were an early form of photography that used metal plates. They are reverse images, and the Billy the Kid tintype led to the mistaken belief that Billy the Kid was a lefty. The myth inspired the 1958 movie "The Left Handed Gun", starring Paul Newman as Billy.
The Associated Press contributed to this report.