Billy the Kid (aka Henry McCarty) lived a brief and violent life before his death in a gunfight aged 21. The second photo of McCarty ever to be authenticated shows him and his posse, the Regulators, playing croquet in New Mexico in 1878.
Collector Randy Guijarro paid $2 for the image in 2010, which is now estimated to be worth millions of dollars. The only other confirmed photo of Billy the Kid, from 1880, sold for $2.3m in 2011.
More: The Guardian