When Jacob Riis published How the Other Half Lives in 1890, it proved to be a milestone in photojournalism, a work of art that actually changed society for the better. As Bonnie Yochelson suggests here, Riis was an activist first and a photographer second, yet the more than 150 images collected in this edition are poignant and haunting masterpieces in their own right. Here are unflinching views of New York's classrooms and prisons, nurseries and graveyards, although some of the most compelling photographs prove to be the shots of everyday people who are willing to look straight at the camera.