Some of the biggest movies of the past decade — including Oz the Great and Powerful, and the third and fourth Transformers films — have been shot in Detroit, where producers can take advantage of Michigan’s generous film incentives, not to mention the city’s abundant empty lots. Along with the movie boom, Motor City has seen the rise of another, more covert industry: amateur photography by people who stake out sets and share their pictures online. When Batman v Superman: Dawn of Justice filmed in Detroit this summer, newspapers and websites combed social media sites, looking for the latest on-set photos — many of which came from a Twitter user named @bananadoc.