How did a New York nanny become one of the great photographers of the 20th century?

Finding Vivian Maier is a documentary about the American nanny who led a wholly secretive life as a photographer and who, posthumously, has been described as ‘one of the greatest photographers of the 20th century’. It’s a good story, which is well told here, and told breezily (83 minutes), which we like. But I’m not convinced the quote from Michael Moore on the poster — ‘Amazing…this should be seen with other people, in the dark, on a big screen’ — is necessarily true. Ms Maier has already been the subject of Alan Yentob’s Imagine strand on the BBC, and this film could just as happily be viewed on TV as in the cinema, I think. You must beware movie posters, particularly if it turns out that one of the producers (in this instance, Charlie Siskel) was also one of the producers for Moore’s Bowling for Columbine. This is how it works.