After you create a message based on 16 "offenses" listed on the website - from vacation shots and pics of kids to #TBT posts - a robot will build and post the image for you. The robot, dubbed Silent B.O.B, posts to Instagram using a stylus paired with an Arduino X-Y plotter to insert and crop the photo, along with a Bluetooth keyboard to type out your caption. Your message is sent out from the @PicNixer account, and the offending friend will get a notification.
Since you can only choose from a list of images and captions, your friend-shaming will probably remain anonymous. The limited choices also prevent your digs from getting too out of hand, which is definitely a good thing. Awesome robot-posting aside, we still might suggest taking a more direct approach with you Instagram intervention.
Update: Well, that was quick. Instagram's shut down the @PicNixer account, effectively bringing the service to a standstill. Head here to see how many photos were nixed before the shutdown. (Hint: It was mostly selfies.)