One of the greatest things to rise out of the existence of the Twitter ecosystem has been all the picture services that allow you to quickly and easily send out pictures to your social graph. And now here they come for Foursquare too. Thanks to the release of the Foursquare API , third-party developers are already starting to take advantage of the location-based service's data, and building things on top of it. Jon Steinberg , who recently joined Polaris Venture Partners as an Executive-In-Residence, and before that worked at Google, helped create one of the first third-party apps using this API , SocialGreat . And now he's at it again, hiring an elancer to create Photocheck.in , an app that allows you to check in on Foursquare simply by sending out a picture.