Notorious Wild West gunslinger Billy the Kid paid 25 cents to have his photograph taken outside a New Mexico saloon in late 1880 or early 1881. That faded picture was sold for $2.3 million.

William Koch, the brother of prominent conservative political donors David and Charles Koch, won with the top bid at the Old West Show and Auction on Denver.

It was not clear what Koch might do with the two-by-three-inch (five-by-eight-centimetre) tintype, the only known adult portrait of the legendary outlaw known as William Bonney, Henry Antrim, Henry McCarty or just “the Kid”.

The gunman, who according to legend shot dead 21 people – one for each year of his life – was himself gunned down by a town sheriff in New Mexico in July 1881.

At least two photographic portraits were taken of Bonney as a school child in Silver City, New Mexico. He also appears in the background of a photograph of a half-dozen cowboys at a ranch near Roswell, New Mexico.