Abstract: Apparatus for labelling a stereophonic signal includes a plurality of notch filters having selected center frequencies to form notches at the selected frequencies in the channels of a stereophonic audio signal. Code generating components produce a coded label signal in the form of one or more code words, with the code being formed of selected signal bursts at the selected frequencies. The coded label signals are inserted into both channels of the audio signal, in the notches formed by the notch filters. The code signal amplitude bears a predetermined relationship to the audio signal amplitude in each channel.

Abstract: In an arrangement for decoding code labels embedded in audio signals by inserting signal bursts at selected frequencies into notch frequencies in the audio signal, problems of speed variations in the device producing the audio signal creating notch frequency variation are overcome by providing a plurality of decoders in parallel receiving an incoming signal, each decoder having notch frequencies incrementally displaced from those of the other decoders.

Abstract: A method for inserting coded information into an image comprising the steps of analyzing the image, identifying the edge regions within the image, determining the strength of the edge region, and producing an edge function which is dependent on the strength of the edge. The edge function is added to the image in order to represent coded information.

Abstract: A method of encoding invisible identification code into an image, which is highly resistant to degradation across communications links, and which does not require the presence of the original image for decoding, comprises analyzing the image and determining strongly featured regions such as edges, and inserting code into such regions by altering the structure of the image in a predictable manner, as for example a concave elliptical insert centered on and aligned with an edge, which alteration is not visible to the eye. When decoding, area of concavity are determined, and a correlation is performed with a predicted insert function to assess whether code has been inserted. A hardware embodiment is described.