Over the last 50 years, Mary Ellen Mark has photographed twins, clowns, patients in a mental hospital, Ku Klux Klan members and Liza Minnelli. She likes to look at people who are used to being looked at, and she uses her camera like Wonder Woman’s golden lasso — as a truth-telling device that peels performance from personality. In one of her most famous photographs, “Tiny” (1983), a Seattle street kid poses in her Halloween costume: a little black dress, little black gloves and a hat with a netted veil. It’s the daintiness of Tiny’s dress combined with her defiance that gives the photograph its charge. Tough Tiny looks afraid.