Abstract: A method of updating a database (211) comprising a fingerprint of and an associated set of metadata for each of a number of multimedia objects, A multimedia object and a set of metadata for the multimedia object is downloaded from a file sharing client (101-105). A fingerprint is computed from the multimedia object, and the computed fingerprint and the obtained set of metadata are included in the database (211). The database (211) can be maintained by a central server (210), or be maintained in a distributed fashion by servers (404) running on the file sharing clients (101-105). The database (211) in this way accumulates plural sets of metadata associated with one particular fingerprint. When a sufficient number of sets has been collected, a definite set can be determined using filtering techniques.

Abstract: An input image is distorted so that it has less correlation to a watermark and the distorted image is subtracted from the input image to provide a preprocessed image. If the correlation between the preprocessed image and a watermark is sufficient then the watermark is detected in the input image. The distortion may be a spatially-variant distortion such as stretching, shrinking, shearing or rotation or the distortion may be a non-linear transforming or filtering such as median, local minimum or local maximum filtering.

Abstract: An improved method and arrangement for detecting a watermark in an information (e.g. image or video) signal are disclosed. The detection is more reliable and less vulnerable to image processing by subjecting the suspect image (q) and the watermark to be detected (w) to Symmetrical Phase Only Matched Filtering (24-28,16) prior to detecting (29) the amount of correlation (d) between said signals.

Abstract: An improved method and arrangement for detecting a watermark in an information (e.g. image or video) signal are disclosed. The detection is more reliable and less vulnerable to image processing by subjecting the suspect image (q) and the watermark to be detected (w) to Symmetrical Phase Only Matched Filtering (24-28,16) prior to detecting (29) the amount of correlation (d) between said signals.

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).