Vivian Maier

The lesson: you do not need permission or an audience to keep shooting. Maier bought a Rolleiflex in 1952, worked as a nanny and caregiver for most of her life, mostly in Chicago after 1956, and left more than 100,000 negatives that almost nobody saw until they surfaced at a thrift auction house in 2007. The waist-level viewfinder of that camera meant she looked down into it rather than raising it to her eye, which helps explain the calm, unguarded faces in her pictures. Her self-portraits are the best place to start: her shadow or reflection turns up in store windows, car mirrors and hubcaps, and they show how much a single walk can yield when you treat yourself as part of the scene.