These days most great events are immortalised by photographs. Far fewer are the cases where the photographer is a driving force in the history he records. Such however was Charles Moore, whose unforgettable pictures both chronicled and propelled America's civil rights movement of the 1950s and 1960s.
The images are as powerful, uncompromising and shatteringly immediate today as when they were taken in black and white half a century ago, on the front lines of the struggle playing out across the segregated South.
They range from the arrest of Martin Luther King in Montgomery to the mobs trying to prevent the enrolment of James Meredith, the first black student at the University of Mississippi in 1962; from the dogs and fire hoses unleashed against protesters in the streets of Birmingham, Alabama, to pictures, menacing and haunting in equal measure, of Ku Klux Klan rallies, where the rustle of the hoods and capes is almost audible.
Mr Moore, who has just died at the age of 79, was a white southerner steeped in the civil rights struggle. He grew up in Alabama, where his father was a Baptist minister who sometimes preached in black churches to denounce the evils of Jim Crow.
After serving in the Marine Corps, and a spell studying photography in California, he returned to Alabama in the mid-1950s to work as a news photographer, working for the state capital's Montgomery Advertiser and Montgomery Journal.
In Montgomery, he met the pastor of the Dexter Avenue Baptist Church, a certain Dr Martin Luther King. Mr Moore was the only photographer on the scene when Dr King was arrested and taken to a local police station. Jumping over the counter, he caught the moment when police manhandled Dr King to the counter to be booked.
The picture bore the hallmarks of Mr Moore's work. As usual he was at the very centre of the action, using a short-range lens that lent his photographs their extraordinary close-up quality. More subtly the action seemed to grow out of the lens, making those who looked at the picture feel as though they personally were involved in what was happening.
Nowhere is that sense stronger than in the photos of the demonstrations in Birmingham, during which Mr Moore was hit in the ankle by a brick someone had hurled at the police. One shows three protesters in a doorway, cowering from a jet of water from a high pressure firehose. By omitting to show who exactly was aiming the hose, it seemed to make every American complicit in the brutality.
By that time Mr Moore was a freelance, working through an agency that sold his pictures to Life magazine. Today, Life is little more than a curiosity, a quaint relic of the golden age of news magazines. But in the early 1960s it reached half the adult US population, and in May 1963 it devoted a dozen pages to Mr Moore's photos of the riots. Later, he drily noted that his pictures were "likely to obliterate in the national psyche any notion of a 'good southerner'".
Mr Moore was a brave man. Though he was injured in the Birmingham riots, he continued to take pictures. On another occasion, he was thrown in jail with a group of drunken angry whites. When he went to Oxford, Mississippi, to cover the Meredith enrolment, other enraged white men forced their way into his motel room.
Gradually, he came to understand the power of the images he caught on camera, and the purpose they might serve. "I wanted to show how awful, how vulgar, how terrible this whole thing was," he told The New York Times in 1999. By any measure, he succeeded.