Abstract: The invention provides methods and related systems for embedding and detecting watermarks in images, such as JPEG or MPEG formatted images as well as other types of image signals. One method receives transform coefficients of the image, and changes the value of selected coefficients to embed watermark data in the coefficients. The changing of the coefficients is controlled such that it both embeds the data and forms an orientation signal that facilitates determination of rotation or scale of the image. Another aspect of the invention is a variation of embedding a watermark in an image. This method receives message bits to be embedded in the image, receives transform coefficients of the image, and maps the message bits to selected transform coefficients. The method changes the value of selected coefficients to embed data in the coefficients.

Abstract: The present invention detects the presence of a watermark in-an image by using a multi-step process. First, the image is examined to determine which regions of the image have characteristics such that there is a high probability that a watermark signal can be detected in that region of the image. Next the regions that have a high probability that a watermark can be detected (in contrast to all regions of the image) are examined to find watermark data. In order to determine the probability of finding watermark data in a particular region of an image, the amount of “variance” in the intensity of the pixels in the region is first examined. For example a region that is entirely white or entirely black has zero variance in luminance. Such a region can not carry watermark data, hence regions with zero or low variance can be eliminated from further processing.

Abstract: Watermark and pattern detection can be improved by compensating for artifacts introduced into an image by a printer and/or scanner through which the image has passed. With the present invention, prior to watermark or pattern detection, the image is filtered or modified to compensate for artifacts introduced by the printer and/or scanner. Some scanners automatically compensate for artifacts introduced by the scanner by using a calibrated tone map. The automatic compensation provides an image from which, a watermark can be easily read. However, generally the user is provided with an interface which can be used to change certain parameters such contrast and intensity. The changes made by the user change the compensation (i.e. the tone map) applied to the image. If the user changes the compensation applied to the image it can affect the ability to read the watermark.

Abstract: Embedding a watermark in an image by changing selected DCT coefficients in the blocks and macro blocks of coefficients which represent the image. The changes in the blocks that comprise each macro block are done in a coordinated manner so that the phase of the watermark signal is preserved across the block boundaries. By preserving the phase across block boundaries, a detectable grid is formed which can be used as an orientation and scaling grid. Furthermore, by preserving the phase across block boundaries the visual artifacts introduced by the watermark are minimized. The bit rate of the image signal is preserved by maintaining a count (referred to as the cumulative change count) that represents the amount that the bit rate has been increased by changes in coefficients less the amount that the bit rate has been decreased by changes in the coefficients.

Abstract: Embedding a watermark in an image by changing selected DCT coefficients in the blocks and macro blocks of coefficients which represent the image. The changes in the blocks that comprise each macro block are done in a coordinated manner so that the phase of the watermark signal is preserved across the block boundaries. By preserving the phase across block boundaries, a detectable grid is formed which can be used as an orientation and scaling grid. Furthermore, by preserving the phase across block boundaries the visual artifacts introduced by the watermark are minimized. The bit rate of the image signal is preserved by maintaining a count (referred to as the cumulative change count) that represents the amount that the bit rate has been increased by changes in coefficients less the amount that the bit rate has been decreased by changes in the coefficients.