Learning that your nanny moonlights as a street photographer would probably come as a wonderful surprise–who doesn’t like a little artistic influence in their kids’ lives? But Vivian Maier kept her work private, and her secret side wasn’t revealed until a man named John Maloof bought an unmarked box of her negatives at a Chicago auction house in 2007. Finding Vivian Maier is the story of how Maloof unearthed over 100,000 of her photographs, taken primarily in Chicago and New York during the 1950s and 60s, and posthumously added her to the canon of 20th century photography. The documentary has found many admirers on the festival circuit, and is popping up for one night only at The Green Building, as part of Gowanus Art + Production’s varied spring programing. Tickets are $7.