Binary image watermarking through biased binarization

This paper presents a watermarking algorithm for binary images. The original binary image is blurred to a gray-level image and we embed the watermark by biasing the threshold in binarization. A loop is used to control the quality of watermarked images and robustness, and a key is generated for extraction. We employ error correction codes to reduce extraction error. This algorithm can be applied to general binary images except dithered images. Experiments show that the distortion in the watermarked image is not obtrusive and the algorithm provides some degree of robustness.