Pinterest and InstaGram are two Photo Sharing sites. According to the twitter numbers Instagram has 1.5M followers compared to Pinterests 569K. If you look further down the Infographic, Pinterest is getting much more mentions probably because of all the latest media hype.

 I think InstaGrams iphone app makes it easy to share and that's why there are much more followers. Maybe Pinterest should come out with its own app for Smartphones and see their twitter followers increase substantially.