The photo of the flag raisers on Iwo Jima has long been an emblem of U.S. efforts in World War II; photos from My Lai still represent the Vietnam war for many. After eight years, however, there is still no single image that has defined the Afghan war. A new PBS/Frontline documentary, "Obama's War," contains footage and images of the war that hasn't been seen on American television screens until now.

The film begins with the death of a U.S. marine, Lance Corporal Seth Sharp, who is cut down by Taliban fire during a battle in Helmand province last summer. We speak with Seth's father, Ric Sharp, and Danfung Dennis, the photojournalist who captured the footage, about the power of images in the Afghan war. Martin Smith, co-director of "Obama's War," also joins us.

[Watch the first 24 minutes of the film here, or visit Frontline's website this evening for the entire piece.]