'The things happening on Tokyo's streets are always fascinating to me," Nobuyoshi Araki told me during an interview in 2012. Though best known for being the maestro of Japanese erotica, Araki has retained a particular love for street photography. Now 75, he still loves to prowl around the streets of Shinjuku and Ikebukuro with his old camera. And he is not alone — many renowned Japanese photographers have launched their careers from the streets of the metropolis. Ihei Kimura was one of the first photographers to stand on the thronging streets of Ginza in the early 1950s, and snap away at the shoppers, those intent on embracing Western culture, ideas and fashion after the dark years of war and defeat. Kimura treated the streets like a studio, and generations of photographers followed his example. As with Araki, they are drawn to the ever-changing cityscape and its constant metamorphoses. What's here today could be gone tomorrow, and magazines such as "Tokyojin" are devoted itself to documenting and archiving the here-and-now of Tokyo streets in their brief and strange glory.

Among this legion of street photographers, however, there are none (that we know of) who have kept their work a secret. To do so would probably defeat the very purpose and meaning of street photography. But over in the U.S., a Chicago nanny named Vivian Maier did just that. She took thousands of powerful street photographs and never let the world know about them. The documentary "Finding Vivian Maier" is a quest to discover the identity of this elusive, mysterious photographer, whose work was never shown during her lifetime and whose talent was literally kept under lock and key for decades.

In 2007, Chicago collector John Maloof paid $380 for a huge case full of old negatives at a local auction. At the time Maloof was studying Chicago's history and he thought the negatives would come in handy. As he scanned them, he became increasingly intrigued about the photographer — but there were no hits when he searched for "Vivian Maier" online.