Now 40 million users strong, digital photo-sharing app Instagram has taken advantage of the photoblog trend and transformed into something of an overnight global success. With the startup earning press for expanding its product to Android users and being snatched up by Facebook's powerful grasp, the tech world is wondering what kind of users are downloading the app and catapulting the brand to the top. Below is a guide on how to recognize the obvious signs of a die-hard Instagram devotee.