1. An image surveillance system comprising: a foreground detecting unit which detects a foreground region based on a difference between pixel information about a background image and pixel information about a current input image; a still region detecting unit which detects a candidate still region by clustering foreground pixels of the foreground region, and determines whether the candidate still region is a falsely detected still region or a true still region; and an object detecting unit which determines whether an object is left behind or taken away, based on edge information about the true still region.