The document describes TagSense, a new approach to automatic image tagging using smartphones. TagSense leverages multiple sensors in smartphones like accelerometers, compasses, microphones and GPS to generate tags for images including who, what activity, and location. It works better than existing techniques like facial recognition since it does not rely on facial features. The system architecture has phones share a password to coordinate sensor data collection when a photo is taken to generate tags without human input. Preliminary tests show TagSense has higher recall than other auto-tagging systems but lower precision.