"A 14-year-old girl stoops and screams above the body of a Kent State University student killed in 1970 by an Ohio National Guardsman.
A police chief executes a Vietcong prisoner in 1968 on a Saigon street.
And an unarmed man in Beijing, China, stands defiantly in front of a column of tanks as they rolled into Tiananmen Square in 1989.
But while these photographs -- chronicling a single, silent moment -- were taken by seasoned photographers, two of whom won Pulitzer Prizes, this time amateur cell phone video is grabbing worldwide attention. It captures the death of a young woman named Neda Agha-Soltan, galvanizing protesters."