I. Introduction
The emergence of resource-rich devices has changed the landscape of mobile sensing with multiple embedded sensors, e.g., accelerometers, cameras, etc. With more than 6 billion mobile subscriptions worldwide, these sensors (collectively) can be used to sense the environment and gather valuable data of unprecedented quality and quantity, practically from everywhere. This new sensing paradigm, Mobile Crowd Sensing (MCS) [1], makes individuals and user communities the focal point of the sensing infrastructure.