HALFTONE WATERMARKING AND RELATED APPLICATIONS

Methods embed a digital watermark into a halftone image. One method derives halftone thresholds from a watermark image, and then uses these thresholds to convert target images into watermarked halftone images. A method for measuring digital watermark strength is used for a variety of applications, such as distinguishing original printed documents from copies. In this method, a watermarked signal is processed to extract estimates of error correction encoded bits embedded into the watermarked signal. Then, the error correction encoded bits are decoded to compute a message payload. The message payload is re-encoded to compute error correction encoded bits. A measure of watermark strength is computed from the error correction encoded bits and the estimates of error correction encoded bits.