1. A method of extracting an image of a moving object from an image inputted successively, said method comprising the steps of: extracting a feature parameter of said inputted image; storing said feature parameter of said input image as a feature paramter of a background image, said feature parameter of said background image being unchanged or slowly changing; transferring said feature parameter of said background image so as to correspond positionally to a feature parameter of an image successively inputted; forming a feature parameter of background image free of any moving object images, based on a weighted mean between said transferred feature parameter of said background image and said feature parameter of said image inputted successively, only said transferred feature parameter of said background image being weighted; and extracting information relating to an image of said moving object from said feature parameter of said image through comparison of said feature parameter of said background image free of any moving object image and said feature parameter of said image inputted successively.