Data hiding for bi-level documents using smoothing technique

In this paper, a method for watermarking on binary images to authenticate the owner or authorized user is proposed. The proposed method makes use of noise suppression patterns which takes into account the smoothness in 5 × 5 neighborhood. It has a moderate capacity of the watermark while preserving very good invisibility to human eyes. The resulted watermarked binary image is an enhancement to the original image in terms of smoothness. The fast computational speed and time complexity makes the method suitable for real-time authentication. Retrieval of the watermark doesn´t require the presence of the original binary document image. However the secret key and the location map information are needed for the retrieval. The watermark used in the algorithm is the gold-like sequence. Discussions on issues in binary image watermarking have also been presented. Experimental results validate the arguments made in the paper.