Mary Ellen Mark, 75, a Cheltenham High School cheerleader who became one of the most influential photographers of her time, died Monday in New York of complications from myelodysplastic syndrome, a blood disease.

Her portraits of celebrities, street people, and prom-goers are familiar to many Americans who saw her work in Life, National Geographic, Vogue, the New Yorker, Rolling Stone, Vanity Fair, or one of her 18 published photo collections.

"She was a world-class photographer whose work captured both the unique soul of her subjects and the humanity that binds us all together," Michael X. Delli Carpini, dean of the Annenberg School for Communication, said Tuesday of Ms. Mark, who received a master's degree from the school in 1964.

Not for her glamorized portraiture nor the cultivated exuberance of selfie culture. Her subjects rarely smiled - which doesn't mean they weren't funny. Her mug-shot double portrait of John Belushi has him raising his right eyebrow in one photo and his left brow in the other. A celebrity portrait of a bearlike Marlon Brando has him mesmerized by a delicate dragonfly. In another, a beetle crawls across his forehead.

"Reality is always extraordinary," was her mantra. And she found the extraordinary both on the fringes of society - among Seattle runaways and Calcutta orphans - and at its red-carpet center, where Hollywood's most-wanted strut.

Ms. Mark could tell an epic story in a single image, as in an ad for Novartis, the pharmaceutical company, showing a young girl bald from chemotherapy holding up a photo of herself with resplendent hair.

Time art critic Robert Hughes called her photo series "Ward 81," made in the maximum-security women's ward of a state mental hospital in Oregon, "a lamentation: one of the most delicately shaded studies of vulnerability ever set on film."

The most profound quality of her work was palpable empathy for her subjects. In Exposure, a 2005 collection of photographs and observations, she wrote of shooting a 15-year-old girl in labor. "Photographing Jeanette was a great learning experience for me," she said of the photos for Children of Desire. "I learned how important it is to stay with a subject, . . . that you can capture more intimate moments by blending into the background."

Equally important was her deep well of compassion. She neither condescended to nor exploited her subjects.

"Her photographs communicated the joy and heartbreak of lives very different from our own," said Kathleen Hall Jamieson, director of Penn's Annenberg Public Policy Center. "Walter Annenberg said one of things he was proudest of was that the school had educated Mary Ellen Mark."

Ms. Mark grew up in Elkins Park, child of a mentally ill father and a mother who "was not a particularly stable person," she said in a 2005 interview. After school, she found a sense of continuity and stability in family photo albums. "I was fascinated by that sense of time stopping and a moment being preserved forever."

Like most preteens, she took snapshots of friends at camp and school; unlike theirs, hers were later repurposed as part of a slide show narrated by Jack Nicholson in the 1971 film Carnal Knowledge, which costarred her close friend Candice Bergen. The silky blonde and the wiry brunette had first crossed paths at Penn in 1963 when Bergen was a freshman and Ms. Mark, who had graduated from the School of Fine Arts in 1962, was at Annenberg.

It was there that she was given a Leica that changed her life. "From the very first moment I took pictures [on the streets of Philadelphia], I loved it," she told The Inquirer in 1988. "The thrill was the idea of just being on a street, turning a corner and looking for something to see. It was just an amazing feeling."

In London in the early 1980s to photograph James Cagney for his last movie, Ragtime, Ms. Mark met filmmaker Martin Bell, who was working on a documentary about the actor. They married in 1982 and went on to collaborate on 1984's Streetwise - Bell's Oscar-nominated documentary about Seattle teenagers that grew out of her assignment for Life - and many other projects.

Ms. Mark received nearly every major academic, artistic, and journalism prize extant, including a Fulbright Fellowship in 1965, a Front Page award in 1980 for Children of Desire, her New York Times magazine series on unwed teen parents, and a 1994 Guggenheim Fellowship.

A photographer's photographer, Ms. Mark never switched to digital cameras. "I'm staying with film, and with silver prints, and no Photoshop," she told The Inquirer in 2008. "That's the way I learned photography: You make your picture in the camera. Now, so much is made in the computer. . . . I'm not antidigital, I just think, for me, film works better."

Ms. Mark is survived by Bell, her husband of 33 years, and countless photographs, including those in the collections of the Los Angeles County Museum of Art, the Whitney Museum, and the Philadelphia Museum of Art.