An optical monitoring system is capable of automatically identifying whether a moving body is a monitored subject based upon information in an optical (i.e., video) image. A moving body detection sub-system images a monitored region and detects a moving body from changes over time in the image of the monitored region. A speed detection sub-system detects the speed of a moving body in the image plane (i.e., speed of the moving body image in the image plane). A scale detection sub-system detects the size of a moving body in the image plane (i.e., size of the moving body in the image plane). A moving body estimation sub-system decides whether a moving body is the monitored subject (e.g., a human being) based on the image plane speed detected by the speed detection sub-system and the image plane size detected by the scale detection sub-system.