A cell block at the now-closed Abu Ghraib prison in Baghdad, a facility notorious for photos released in 2004 showing U.S. soldiers torturing and humiliating inmates. Karim Kadim/AP hide caption

itoggle caption Karim Kadim/AP

Shiite fighters and Sunni fighters, who have joined Shiite militia groups known collectively as Hashid Shaabi ("Popular Mobilization") to fight the Islamic State, gesture Tuesday next to former Iraqi President Saddam Hussein's palaces in the Iraqi town of Ouja, near Tikrit. Thaier Al-Sudani/Reuters/Landov hide caption

itoggle caption Thaier Al-Sudani/Reuters/Landov

Heavy smoke rises following an airstrike by the U.S.-led coalition aircraft in Kobani, Syria, during fighting between Syrian Kurds and the militants of the self-declared Islamic State in October 2014. Gokhan Sahin/Getty Images hide caption

itoggle caption Gokhan Sahin/Getty Images

Shiite militiamen pose with their banner (right) next to a captured — and upside-down — ISIS flag (left) in Tikrit, Iraq. Militias are bolstering Iraqi forces in a major operation to retake the city from the self-proclaimed Islamic State. Mohammed al-Mozani/AP hide caption

itoggle caption Mohammed al-Mozani/AP