1. A supervising system for image supervising a supervising area by picture images comprising: an image forming device taking pictures of an image in the supervising area, even in a condition that an image forming device is covered, put an obstruction, sprayed, or sticked with drops of rain, an illuminance sensor detecting an illuminance in the supervising area, a feature extracting portion extracting an amount of feature in the image as taken pictures, a first portion for detecting change of time detecting change of time in the amount of feature as extracted, a second portion for detecting change of time detecting change of time of the illuminance as detected, and a scheme judging portion detecting a scheme against the image forming device in accordance with the change of time in the amount of feature and the change of time in the illuminance as detected.