Vivian Maier never showed her photographs to anyone while she was alive.  After her death, some of her images were put online and she was quickly acclaimed as one of the foremost street photographers of the 20th century.  In this exclusive clip from “Finding Vivian Maier,”  John Maloof, who bought her possessions at an auction, talks about the mystery of the nanny who turned out to be a photographer of immense gifts and humanity.  The documentary, “Finding Vivian Maier” is on VOD and in selected theaters.