On an autumn day in Beijing, artist Deng Yufeng led a group of volunteers on a carefully choreographed walk through the Chinese capital’s streets. In one block, the group had to inch sideways in a line, hand in hand. In another area, the volunteers had to bend down and crouch next to a row of bicycles. The antics were part of Deng’s mission to “disappear” from closed-circuit television surveillance cameras, which are increasingly in use by authorities in many Chinese cities. (Photo: Deng…