“…From visual sensors, wearable sensors, to humans as sensors [31], multiple sensor media streams constantly provide observations on the real world that are utilized in many aspects of our life: from industrial process control, robotics, surveillance, smart houses to situation awareness [34]. Examples of sensors include (a) physical sensors like cameras, accelerometers, gyroscopes, mobile phones, RFID tags, temperature sensors, humidity sensors and (b) social sensors like social networking sites containing user-generated content reporting events in all kinds of formats (text, image, video, etc.).…”