In 1955, shortly after Emmett Till was murdered by white supremacists in Mississippi, his grieving mother distributed to the press a gruesome photograph of his mutilated corpse. Asked why she would do this, she explained that by witnessing with their own eyes the brutality of segregation and racism, Americans would be more likely to support the cause of racial justice. "Let the world see what I've seen," was her reply. The publication of the photograph...