On the eve of it going public, I wrote about Twitter's new embrace of images:
All those images are merely bait for what Twitter is really going after: the social-network fuel known generically as "engagement." Likes, hearts, comments, favorites, retweets — whatever form engagement takes, the result is a rush of dopamine straight to the user’s head. It’s the magic that makes people return to places like Facebook, Instagram, and Tumblr multiple times throughout the day. Each of those networks persuaded its users that it was a place that they would be showered with validation. And with that validation came new users by the tens of millions.