Pictured above: Jacob Riis’s “ I Scrubs” — Little Katie from the West 52nd Street Industrial School,” 1891-1892. (Jacob Riis/Museum of the City of New York/Courtesy of Library of Congress)

He was heralded with pioneering a particularly stark and revealing brand of photojournalism, but Jacob Riis never even considered himself a photographer.

Toiling in New York’s Lower East Side before the turn of the last century, the crusading newspaperman used the newly developed breadbox-size camera to shine light on overcrowding, poverty and squalor in the tenements.

And using the flashgun methods of illuminating nighttime shots, Riis also set at least three fires, according to the current Library of Congress exhibition “Jacob Riis: Revealing ‘How the Other Half Lives.’ ”

The exhibition combines the Riis papers in the library collection with a number of photos, once thought long discarded, that were found in an attic and donated to the Museum of the City of New York, which is co-presenting the show.

Riis (1849-1914) may have had an affinity for immigrants since he, too, had moved to the United States from his native Denmark in 1870, spending three years walking the East Coast until he found a job in New York newspapers. He couldn’t ignore the squalor and overcrowding all around him, so he published his findings in the paper, in magazines of the day such as Scribner’s and, eventually, in such influential books as “How the Other Half Lives” and “The Children of the Poor,” which galvanized reformers to improve conditions.

Riis became a friend of President Theodore Roosevelt’s and an in-demand speaker nationally who would bring his newfangled visual device: the “magic lantern” that cast his striking photographs onto screens in the days when motion pictures were just starting.

A re-creation of his magic lantern presentations is part of the exhibition, as is paper-print film footage of the Lower East Side at the turn of the 20th century.

“ ‘I Scrubs’ — Little Katie from the West 52nd Street Industrial School,” 1891-1892: The signature portrait of “Jacob Riis: Revealing ‘How the Other Half Lives’ ” is this haunting look at a 9-year-old who seemed old before her time. “A sober, patient, sturdy little thing,” Riis called her, “with that dull life wearing on her day by day.” Katie could go only to one of the 21 industrial schools the Children’s Aid Society in New York City established from 1854 to 1874, when she didn’t have to cook, clean and keep house for three older siblings. When Riis asked about her work, she replied, “I scrubs.”

“Bandits’ Roost,” with Richard Hoe Lawrence and Henry G. Piffard, 1887-1888: Riis wasn’t above posing his subjects, as he did these Italian immigrants in an alley at 59½ Mulberry St. Working with Lawrence and Piffard, with whom he shared the credits early in his career, Riis took this photo with a stereoscopic camera.

“In the Sun office, 3 AM,” 1891-1892: Part of the scenery at the New York Sun in the 1890s were newsboys who sometimes caught shut-eye and shelter in the office. But they were not orphans, Riis pointed out in his writing. Instead, they were “children with homes who contribute to their family’s earnings and sleep out, if they do, either because they have not sold their papers or gambled away their money at ‘craps’ and are afraid to go home.”

“Five Cents a Spot,” 1888-1889: The going rate for lodging houses in those days was seven cents a night for a bed, but it cost only five cents a night to sleep illegally on the floor. This photo was taken during a raid on an illegal lodging house by the sanitary police, a place Riis described thus: “In a room not thirteen feet either way slept twelve men and women, two or three in bunks set in a sort of alcove, the rest on the floor.” Because photographs were not easily transferred to the printed page in the 19th century, they were often rendered as woodcuts, as was this image when it appeared in Scribner’s magazine in December 1889.

Jacob Riis: Revealing “How the Other Half Lives” through Sept. 5 at the Library of Congress’s Thomas Jefferson Building, 10 First St. SE. Free. 202-707-5000 or loc.gov.