An apparatus for eliminating background noise from a security marker authenticating system including a first sensor for capturing an image of a background of the security marker; a light source for illuminating the security marker; the first sensor or a second sensor or both captures a plurality images of the optical response of the security marker; a computer which averages the plurality of optical response images; the computer smoothes the background image; and the computer subtracts the smoothed background image from the average of the plurality of optical response images.