Instagram, the popular photo-sharing mobile app, has been quite a craze among the photo-sharing enthusiasts as it is essentially a social network built around modifying photos --- more like a photos-centered Facebook!

Instagram - which social networking giant Facebook has recently acquired in a whopping $1 billion cash and stock deal - is actually about much more than doctored up photos shared by the users; and has witnessed a meteoric rise in usage ever since it was launched two years back by its co-founder and CEO Kevin Systrom.

Largely giving the feel of Facebook, sans the clutter, Instagram allows users to post photos only, while the Facebook social network allows them to post hordes of things, including links, quizzes, and personal opinions and expressions.

Since Instagram virtually lives on the phone, the pictures which the users post on the photo-sharing site are basically the spontaneous photos - that too, only square shots, to ensure a uniform and uncluttered appearance - which they have clicked via their camera phones, rather than the pictures of special occasions clicked using a standalone camera.

The phone-centric feature of Instagram also implies that users cannot browse or add photos from its website; and can only do so if they link the service to either Facebook or any other social network.

Meanwhile, so far as sharing of the photos is concerned, Instagram works quite like Twitter --- users can follow any number of individuals or brands, and their photos automatically appear on other users' personal Instagram stream!