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

Iraq's push into Tikrit follows its retaking of the nearby town of al-Alam on Tuesday. There, a woman welcomed a relative who is fighting with a militia that's backing Iraqi troops. Thaier al-Sudani/Reuters /Landov hide caption

itoggle caption Thaier al-Sudani/Reuters /Landov

Iraqi security forces and Shiite fighters fire artillery during clashes with ISIS militants in Salahuddin province. The push to retake Tikrit is being aided by Iran, which is providing rockets and other support to Iraq. THAIER AL-SUDANI/Reuters /Landov hide caption

itoggle caption THAIER AL-SUDANI/Reuters /Landov