1. A method of electronically analyzing the image of an illuminated object for significant changes in the light level of a predetermined amount which comprises the steps of: storing in a digital electronic network an electronic look window having the contour information of a standard object derived independently of the object to be analyzed; moving the object to be analyzed in front of a source of illumination; projecting the illuminated object image onto image sensing means to produce signals indicative of the light levels of the sensed image of the illuminated object; feeding the sensed image signals of the illuminated object into a signal processing networks; feeding synchronizing information from the image sensing means into the network containing the electronic look window; electronically relating the two networks to superimpose the electronic look window contour of a standard object on the signals derived from the sensed image signals; and evaluating to a reference level only the signals which appear within the electronic look window and are produced by the light levels of the sensed image.