I was trying to work out the security of an system that used the polarized LCD panel over an OLED display (the point being that you can only block certain pixels) and the pixels are either on or off (white or bleck). When the device is enabled someone a random key (lets aim for the best, one time pad quality) is generated that will block a random set of pixels and allow others to pass through unaffected. What is shown is the original display with some pixels blocked off. The blocked off pixels are known only by the content generator and the filter (not the device containing the OLED display). My question is how do I model this system in order to determine what sort its cryptographic quality.