The story of a heretofore unknown photographer, much of which remains a mystery, will eventually be folklore, not only because her talent remained in the shadows until after her death at age 83 – but for the unlikely fashion in which her work came to see the light.

In a twist on one of those masterpiece-found-in-the-attic tales, a Chicago real-estate agent named John Maloof came across a box of negatives at an auction in 2007. Hoping they were historic photos of his Portage Park neighborhood, he paid $400 and stored the 30,000 negatives away for later review. When he took a look, what he saw, though not what he expected, was captivating – prompting him to hunt down what turned out to be another 70,000 pictures. When he posted some of the images on Flikr, his instinct regarding the greatness of the pieces was confirmed; hundreds of e-mails followed.

The creator of those photos, Vivian Maier, had died shortly before Maloof could contact her after his big find. (It wasn’t until 2009 that he discovered her name, scribbled on an envelope buried in one of the batches of film.) It turned out she had been a nanny for several affluent families in the Chicago area throughout the ’50s to the early ’90s, toting her Rolleiflex on assorted trips and outings, quietly capturing just some of the images now featured in the book Vivian Maier: Street Photographer  — released this month and compiled by Maloof after the incredible acclaim that followed their widespread dissemination on the Internet, along with subsequent exhibitions in Norway, Denmark, and England.

In approaching Maier’s work, one is struck by the naturalistic similarities to the craft of the Depression-era photographer, Walker Evans: the second-in-time spontaneity, the cut-to-the-heart facial expressions, the prosaicness of the everyday street scene taken to a sublime level. Maier photographed people from all walks of life, young and old, black and white, rich and downtrodden. Like all great street photographers, she understood that moments matter.

And the expansiveness of what would now be called her portfolio shows that her curiosity about what lay behind those moments never wavered.

Her pictures are not titled and can just be described by their subjects – faces, places, and instants that only an outstanding eye could grasp: the simple sidewalk scene of a group of women shot from the waist down, with a pair of rotund legs unexpectedly revealed by a sudden burst of wind; a quizzical glance by a bystander at a man inexplicably attired in a hat, jacket, and boxer shorts; an aging, wealthy doyenne in mink, her haughty look implying impatience with the camera.

There’s irony in the fact that Maier’s newfound reputation owes itself to the networking of the digital age. Described as a highly private woman, she never made a point of sharing her secret passion with anyone, and were it not for Maloof’s accidental discovery, and her photography subsequently going viral, the treasure trove would sadly have remained undetected – and unlauded. As it is, the Maier archives are a unique contribution to the annals of American photography.