The exhibition showcases 17 rare photographs taken by American photographer Al Rockoff and French photographer Roland Neveu.
Now 54, Him Huy said Monday he had been recruited as a young man the year before the capital fell.
Seng Theary filed the complaint against former Khmer Rouge commanders Meas Mut and Sous Met.
The Trial Chamber is now deciding who else among thousands of applicants will stand as witness when the trial begins.
Defense lawyers say they need specialist doctors to evaluate the condition of the accused before a hearing is fully set in motion.
Seng Theary names former Khmer Rouge commanders Meas Muth and Sou Met, in an effort to move the court forward on cases 003 and 004.
This is the second day of hearings for Duch, who was tried in 2009 in the first test of the UN-backed court.
Duch, the former Tuol Sleng chief's sentence was reduced to 19 years because of time served and other factors.
Duch, was found guilty by the Trial Chamber of atrocity crimes that included crimes against humanity.
In their decision Thursday, the Trial Chamber said the motion lacked evidence and reasoning.
Defense lawyers have already requested shorter days for hearings, claiming the defendants are old and cannot sit through full days.
Three former survivors of Tuol Sleng prison, are anxiously awaiting a final hearing on its chief administrator, Duch, later this month.