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

Dura Europos, a Roman walled city in eastern Syria, dates back to 330 B.C. The main gate is shown here in a photo from 2010. It's one of the many important archaeological sites militants of the self-styled Islamic State have ransacked and damaged. EPA /Deir Ezz-Zour Antiquities Department/Landov hide caption

itoggle caption EPA /Deir Ezz-Zour Antiquities Department/Landov

These pop-up targets are part of an advanced drill, named "friend or foe," that tests shooter reaction times. Some targets have a camera, and others, like these pictured, have a gun. The shooter must decide within seconds whether to shoot. Deborah Amos/NPR hide caption

itoggle caption Deborah Amos/NPR

The most recent propaganda videos from Boko Haram have higher production values than in the past and other similarities to ISIS-produced videos. Boko Haram/Sendvid hide caption

itoggle caption Boko Haram/Sendvid

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

Members of Iraqi security forces drive toward an area south of Tikrit, Iraq, over the weekend. An Iraqi force has launched a military offensive, hoping to push ISIS out of Tikrit. AHMAD AL-RUBAYE/AFP/Getty Images hide caption

itoggle caption AHMAD AL-RUBAYE/AFP/Getty Images

Then-U.S. ambassador to Iraq Christopher Hill (right) tours the Mosul Museum of History in May 2009. This week the self-declared Islamic State posted a video online that showed militants going through the museum, pushing over statues and smashing artifacts with sledgehammers. Mujahed Mohammed/AFP/Getty Images hide caption

itoggle caption Mujahed Mohammed/AFP/Getty Images

A playground can be seen outside an address in London where Kuwaiti-born London computer programmer Mohammed Emwazi is believed to have lived. Emwazi has been identified as masked ISIS militant "Jihadi John." Niklas Halle'n/AFP/Getty Images hide caption

itoggle caption Niklas Halle'n/AFP/Getty Images

Jordan's election laws make it impossible for any one political party to build a strong bloc in Parliament. Observers say that's one reason for the country's weakness — and for the growing appeal of the messages used by militants of the self-proclaimed Islamic State. Khalil Mazraawi/AFP/Getty Images hide caption

itoggle caption Khalil Mazraawi/AFP/Getty Images

A central figure in videos released by the self-declared Islamic State has been identified as a man from West London. He's seen here dressed in black, threatening Japanese captives Haruna Yukawa (right) and Kenji Goto. Kyodo/Landov hide caption

itoggle caption Kyodo/Landov