Patent ID: 8019201

Claim:
A method of generating or modifying a programme signal to provide protection against copying on a programme recording device, the method comprising the steps of: receiving a programme signal or information for generating a programme signal divided into lines of information, said signal having horizontal synchronisation pulses and vertical synchronisation pulses for synchronising the programme on the screen of a receiver; adding a pulse into said programme signal during the horizontal blanking interval of lines that contain picture information and into lines in the vertical blanking region; adding a first modulation signal to vertical synchronisation pulses of said programme signal; adding a second modulation signal to lines of picture information in the vicinity of said vertical blanking region at the bottom of a frame of said programme signal; wherein said pulse, and said first and second modulation signals added to said programme signal are sufficient such that when said signal is copied by the recording device, interference is produced in the reproduction of the copied signal that is not visible in the reproduction of an uncopied programme signal.