Britain, France, Qatar, Saudi Arabia, Turkey and the United States are holding an exhibit at the United Nations of graphic photos taken in Syria by a former military police photographer that show what appear to be evidence of brutal torture.

About two dozen of some of the 55,000 photographs taken — some showing eye gougings, strangulation and long-term starvation — went on display at U.N. headquarters in New York this week as the conflict in Syria enters its fifth year.

Former war crimes prosecutors have described the pictures as "clear evidence" of systematic torture and mass killings in Syria's three-year-long civil war. The photographer has been identified by the code name "Caesar." The pictures were smuggled out of Syria between 2011 and mid-2013.