Thousands? Tens of thousands?

How many faces did she find in obscurity -- and immortalize in celluloid?

From India to Iceland. Africa and Asia. Across the Middle East and Europe. In mental institutions and leprosy wards. Circuses. Bordellos. Street corners everywhere. Hers was a legend earned out in the world, over 50 years, without abandon.

She sought the "unfamous" and photographed them with empathy and technical mastery.

But none like Erin "Tiny" Blackwell, the 13-year-old prostitute she found among Seattle's vagrant youth while on assignment for Life magazine in 1983.

"Mary Ellen saw this little girl dressed like a woman get out of a car in a parking lot alongside the Monastery nightclub. Mary Ellen instantly knew she would be the star of the photographs. Because Mary Ellen was always looking for that. There it was," said Martin Bell, Mark's widower and longtime collaborator.

Mary Ellen Mark and her husband, Martin Bell, discuss a photo shoot in New Orleans in April. Mark passed away in May.

"It" is a presence on camera. To be unafraid to lay bare one's individuality and essence -- vulnerabilities and strengths alike.

Mark's assignment evolved into a 30-year collaboration between her and her new husband.

Bell directed the Academy Award-nominated documentary "Streetwise," which chronicles three months in the life of Tiny and the rambunctious community of runaway teens in a pre-Starbucks, pre-Amazon Seattle. A follow-up film, encompassing scenes from Blackwell's life over the three decades since "Streetwise," will be released with Mark's final book of photography later this fall.

That collection -- "Tiny, Streetwise Revisited" -- captures the vicissitudes of Blackwell's life from poverty and drug addiction to motherhood and stability. Its incredible scope represents the dedication of a photographer whose work is imbued with a palpable compassion, and the generosity of a subject willing to unclothe realities of life on the margins of society.

It was there -- with the down-and-out and the cast-off -- that both Mark and Blackwell felt at ease. Mark as the gritty photographer who found beauty and dignity in the mundane and brought a voice to the voiceless. And Blackwell, despite the degradations of addiction and desperation, as an indefatigable survivor. A transient by choice.

Mark and Bell, who never had children, offered to bring 14-year-old Blackwell to New York to live with them. The free-spirited teen refused their one condition: to enroll in school.

"Tiny is very smart. The street was a choice for her." Bell said. "She loved the freedom."

The forthcoming book was edited by Mark before her death in May. Its photographs span 31 years, nearly all of Mark and Bell's marriage.

"You see Tiny's life unfold in the book, for better and worse," Bell said. "But we could also see ourselves growing older."

The films and photo collections were the collaboration of three kindred spirits.

"Tiny and Mary Ellen were a lot alike," Bell said. "Stubborn. Smart. Independent. They understood each other."

Mary Ellen Mark was a legendary portrait photographer. "Tiny, Streetwise Revisited" will be released through Aperture.