@ocugwu takes the road less queried.

With over 47 million users, a long-awaited recent expansion to Android and a big move to Facebook earlier this month, Instagram is spreading like dye through a Polaroid. If you haven't yet been lured by the photo-based social network, peer pressure to join its retro-glam ranks is only mounting. The app already contains multitudes—scores of pro-am photographers of all shapes, colors and creeds who have accepted its central promise: to replace a Twitter/Facebook world of self-consciously composed sentences with a brave new world of self-consciously composed and carefully filtered photographs.

On Instagram, every shot is a self-portrait. Herewith, a working guide to the ecosystem's most notorious types.