Twitpic's Face Tagging Shows How Twitter Could Beat Facebook

Twitter's powers always seem to grow in surprising ways, simultaneously via organic developments and third-party apps. Like this latest one for example, a feature of Twitpic that helps Twitter rival Facebook: Face tagging. 

Twitpic's system is completely familiar to anyone who's ever tagged someone's face in systems like Flickr or Facebook--you submit a picture of someone, then manually select the portion of the image that corresponds to the person. A little dialog box pops up, prompting you...