Unidentified Cambodian prisoner, chained at the ankle, photographed outside S-21 prison in Phnom Penh. Although nearly 30,000 people were imprisoned at S-21 and later killed, only 7,000 photographic negatives remain, the vast majority made on 6x6 film. The prison photographer Nhem Ein was trained in Shanghai in 1975-6 by Pol Pot's Chinese patrons, when he was only 15 years old. Photo: © Tuol Sleng Museum of Genocide