1. An apparatus for monitoring hand washing comprising an input device in front of which a subject places his or her hands after he or she has applied and spread a layer of soap or detergent over the front and back of his or her hands, said input device converting light reflected from the soap and subject's hands into an optical image, a device for digitizing the optical image into a digitized image with a plurality of pixels, a computer having an input for the digitized image and an output for a report, a reference feature that distinguishes the soap from the subject's hands, said reference feature in the computer, an algorithm executed in the computer that compares the digitized image, pixel by pixel, with the reference feature and accumulates the number of pixels that match the reference feature, indicating the area to which soap is applied, and the number of pixels that do not match the reference feature, indicating the area of the hands to which soap has not been applied, calculates whether the number of pixels matching the reference feature out of the total number of pixels matching the reference feature plus the number pixels not matching the reference feature is greater than a predetermined level of coverage, and creates a report sent through the output.