THE only known authenticated portrait of the notorious outlaw Billy the Kid has sold for $2.3m (1.4m) at auction in Denver, in the US state of Colorado. The tintype - an early form of photo using metal plates - is believed to have been taken in 1879 or 1880 in Fort Sumner, New Mexico. It depicts the gunfighter in rumpled clothes and a hat, gazing at the camera and holding a Winchester rifle. The tintype was bought by private collector William Koch. It went for some six times the estimate - making it the most expensive piece ever sold at Brian Lebel's Annual Old West Show & Auction, said auction spokeswoman Melissa McCracken. BBC