Iraqi security forces and allied Shiite militiamen look for Islamic State extremists in Tikrit on Tuesday. Iraqi forces were going house-to-house in search of snipers and booby traps. Khalid Mohammed/AP hide caption

itoggle caption Khalid Mohammed/AP

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