By Dan Gilgoff

Tramping through New York's grim tenements and lodging houses in the mid- 1880s, police reporter Jacob Riis felt words alone could never convey the depth of urban squalor. With the advent of magnesium powder flash a few years later, his wish came true. Lugging a frying pan and a revolver to spark the flash, Riis snapped the first shots of the slums that harbored three quarters of the Big Apple's population–one Lower East Side ward packed in 334,000 people per square mile.

Riis's photos, published in Scribner's Magazine and in his book How the Other Half Lives, shocked the bourgeoisie and its politicians into action. Crime-ridden lodging houses folded, lights were mounted in tenement hallways, and the city was linked to a clean water supply. The clumsy amateur photographer–Riis set two buildings on fire and nearly blinded himself in another accident–established the camera as a means to rally society's conscience. In a crusade against child labor 20 years later, a science teacher named Lewis Hine drew on Riis's strategy of shooting photos of the downtrodden. Occasionally posing as an insurance salesman, Hine captured crippled victims of mill accidents and boys blackened by coal mine soot for the National Child Labor Committee. His 5,000 shots of young workers helped pit politicians against the practice of child labor. But while Riis's lens usually looked down at his subjects, Hine set his camera closer to the ground, ennobling the people he photographed. "Riis's images are so powerful because they are so ugly," says David Jacobs, a University of Houston art professor. "Hine's subjects are still victims, but they're given a presence and a stature as individuals."

In the '30s, Hine's shooting style evolved further within the Photo League, a group of young New Yorkers charged by creed with a "duty of recording a true image of the world." League photographers panned the overt social prescriptions of Hine and Riis. They "questioned whether you had to show somebody who was down and out in order to elicit sympathy," says Brian Wallis, chief curator at the International Center for Photography in New York. While the league's work didn't directly spark reforms, it set a social realist course–what members called "straight photography"–for a new generation.

The league's membership shriveled after it was tagged as a possible Communist front in 1949, but its model for confronting reality resurfaced in the 1960s. While Southern blacks had been organizing for years to stamp out segregation and win voting rights, the civil rights movement didn't explode until May 1963, when emotionally powerful photographs of demonstrators in Birmingham, Ala., facing dogs and fire hoses, circulated around the world. "I wanted to show the appalling violence of dogs biting people because of the color of their skin," says Charles Moore, who shot the Birmingham demonstrations for Life magazine. "In the minds of Americans, it was a turning point."

Later in the decade, the Vietnam War–in which journalists and photographers were given extraordinary free rein–provided a stream of intimate, gruesome portraits that hadn't accompanied earlier military campaigns. "Americans couldn't recognize their own image of themselves in a photo of a young girl being bombed with napalm," says Anne Tucker, curator of photographs at the Museum of Fine Arts in Houston. "Those photographs had a great deal to do with the swing in public opinion about what was going on." After Vietnam, the U.S. military largely restricted wartime news media to press pools.

But photographers gained ground in other areas. "Photographers today are focused more on critical political issues that are harder to get at than war, famine, or genocide," says Wallis of the ICP. New York photographer Donna Ferrato began pointing her lens at domestic violence 20 years ago, when she witnessed a husband attacking his wife–and captured it on film. "Back then the attitude was that if the woman is being beat, she probably likes it, or else she would leave," says 52-year-old Ferrato. "I was convinced no one would know what a battered woman went through until people could see her face." Ferrato couldn't find a publication that would carry her photos until 1986, when the Philadelphia Inquirer devoted two issues of its Sunday magazine to domestic violence. Since then, her work has appeared in many magazines and books. "By putting a face on the issue," she says, "I got people interested." Jacob Riis, doubtless, would agree.