From the website:
The 114 photographs on this site are from Pol Pot's secret prison, codenamed "S-21" during his genocidal rule (1975-79). Between 1-2 million Cambodians (and many thousands of foreigners) were starved to death, were tortured, or killed, during his brutal reign of terror.
When the Vietnamese invaded in 1979 the S-21 prison staff fled, leaving thousands of written and photographic records. Altogether more than 6,000 photographs were left; the majority have been lost or destroyed.