The present invention provides methods and systems to authenticate identification documents. The input transmit signal is coupled to a digital-to-analog converter and includes a plurality of independent spread spectrum channels. The method includes iteratively calculating the minimum required backlight intensities that will allow all color points of an image to be represented by the display. A second datapath with the server is associated with a second party. Advantages: the second module can be distributed independently from the first module and from the mobile device.