Analog encryption schemes are infinitely interesting to revisit today. The ingenuity of these folks trying to create an unbreakable encryption scheme with limited resources of 80's and 90's never ceases to amaze me. BTW A piece of software exists that can generate images encoded in various ways, that are supposed to be compatible with original hardware: http://cryptimage.vot.pl/cryptimage.php I have yet to lay my hands on some decoder and try this out myself.