Patent ID: 8032006

Claim:
A method of modifying an analogue video signal to impair analogue to digital conversion of the signal, the signal comprising a plurality of horizontal synchronization pulses, each adjacent a respective back porch, the method comprising: receiving an original video signal for modification; modifying at least one of the horizontal synchronization pulses from its original form to have a greater or a smaller amplitude over at least a part of the pulse width; modifying the region of the signal following the horizontal synchronization pulse, either in the back porch or adjacent to it, from its original form, by inserting a first pulse into lines which appear in the overscan region of the signal, wherein the first pulse is a wave having a frequency in the range 1 MHz to 6 MHz; and outputting the modified video signal, wherein the modified video signal is such that the modified video signal interferes with the operation of an analogue to digital video conversion system to such an extent that, if a digital signal is output, the output digital signal has a reduced quality on playback in comparison to the original analogue video signal.