Abstract: Method of detecting a watermark embedded in a signal (S), in which a plurality of frames of the signal (S) is combined to a detection set (Dj) for one detection event. According to the invention, the reliability of watermark detection is enhanced by using non-consecutive frames to form the detection set (Dj). The invention also relates to an apparatus (2) for recording and/or playback of a signal, and to a system for broadcast monitoring, comprising such a watermark detector (24).

Abstract: A digital image signal is watermarked by locally changing geometric features of the image. The watermark consists of a pseudo-random, dense subset of image pixels, e.g., a pattern of lines (20). A number of significant image pixels (21,22,23), i.e., pixels which give the highest response to a predetermined processing operation, is determined and then moved (24) to the vicinity (&dgr;) of the line pattern. As a result of this “warping”, the majority of significant image pixels (21,22) is eventually located within the vicinity of the line pattern. At the receiver end, the most significant pixels of an input image are again determined. The image is a watermarked image if a statistically high percentage lies within the vicinity of the line pattern.

Abstract: A method and arrangement for embedding a watermark in an image are disclosed. The watermark consists of a pseudo-random, dense subset of image pixels, e.g. a pattern of lines (20). A number of salient image pixels (21-26), for example, local extremes, corners or edges, is identified and it is determined whether they lie on (i.e. within a vicinity &dgr; of) the line pattern (21-23) or not (24-26). In an unwatermarked image (FIG. 2A), the number of most salient pixels (21) lying on the watermark is substantially the same as the number of most salient pixels (25,26) not lying on the watermark. The image is watermarked (FIG. 2B) by modifying the saliency of the salient pixels in such a way that a significant majority (21,23) of the most salient pixels (21,23,25) is eventually located within the vicinity of the line pattern.

Abstract: Recently developed methods for copy protection rely on a watermark detector to judge whether multimedia content can be copied or not. In such copy protection schemes, a watermark detector examines the multimedia content and outputs a signal (D) indicating whether a watermark is present or not. Known watermark detectors determine a decision variable (y) indicating to which extent the watermark is present, for example, the amount of correlation between the input signal and a reference copy of the watermark to be detected. The watermark is detected if the decision variable exceeds a predetermined threshold (y2). Such a detector is vulnerable to an attack which is described in this patent application.

Abstract: A method and arrangement for detecting a watermark in an information signal. The method may include the steps of computing the correlation (dk) of the watermark (Wi) and the information signal (e.g. an image Q) for a plurality of positions (k) of the watermark with respect to the information signal, and detecting whether at least one of the respective correlation values exceeds a given threshold. The step of detecting may include determining the standard deviation (&sgr;d) of the respective correlation values (dk), and setting the threshold to a given multiple (T) of the standard deviation. The multiple (T) is derived form a desired false alarm rate (watermark detected when there is none, or no watermark detected when there is one).

Abstract: A watermark detector is disclosed to judge whether multimedia content can be copied or not. The watermark detector examines the multimedia content and outputs a signal indicating whether a watermark is present or not. A decision variable indicating to which extent the watermark is present is determined, for example, the amount of correlation between the input signal and a reference copy of the watermark to be detected. The watermark is detected if the decision variable exceeds a predetermined threshold (y2). The detector also generates a random output signal for a predetermined range of decision values between the threshold (y2) and a further threshold (y1).

Abstract: A digital image signal is watermarked by locally changing geometric features of the image. The watermark consists of a pseudo-random, dense subset of image pixels, e.g., a pattern of lines (20). A number of significant image pixels (21,22,23), i.e., pixels which give the highest response to a predetermined processing operation, is determined and then moved (24) to the vicinity (&dgr;) of the line pattern. As a result of this “warping”, the majority of significant image pixels (21,22) is eventually located within the vicinity of the line pattern. At the receiver end, the most significant pixels of an input image are again determined. The image is a watermarked image if a statistically high percentage lies within the vicinity of the line pattern.

Abstract: A digital image signal is watermarked by locally changing geometric features of the image. The watermark consists of a pseudo-random, dense subset of image pixels, e.g., a pattern of lines (20). A number of significant image pixels (21,22,23), i.e., pixels which give the highest response to a predetermined processing operation, is determined and then moved (24) to the vicinity (&dgr;) of the line pattern. As a result of this “warping”, the majority of significant image pixels (21,22) is eventually located within the vicinity of the line pattern. At the receiver end, the most significant pixels of an input image are again determined. The image is a watermarked image if a statistically high percentage lies within the vicinity of the line pattern.