Pinterest may have passed Twitter in popularity in the U.S. according to new figures out last month from Pew, but globally the social network to watch may be Facebook-owned Instagram. According to research published today by the GlobalWebIndex, Instagram is growing the fastest of all social media sites worldwide, increasing its active user base by 23% in the last six months.

From my own observation, the interesting thing about the growth of Instagram is that people aren’t using it purely as a photo sharing app - its also a communication tool, with a thread anchored by an image that might not actually be a photo.