An image transmission method, image anti-duplication method, image anti-duplication device, and image recording medium in which information for anti-duplication control is superimposed on a video signal without deterioration of the resultant video signal and the information is extracted accurately and quickly to perform anti-duplication control. An output device starts generation of pseudo-noise (PN) corresponding to a PN code start timing signal generated based on a video sync signal. One chip interval of the PN code is divided into a plurality of divided chips corresponding to a PN code inversion timing signal HT, and an original value of a chip is inverted on an alternate one divided interval to generate a PN inversion code. An anti-duplication control signal is subjected to spectral spreading using the PN inversion code and superimposed on the video signal. In the recording device which receives the video signal from the output device, inversion spectral spreading is performed based on the PN inversion code generated in the same way as that generated in the output device.