Watermarking text document images using edge direction histograms

This paper proposes a novel watermarking algorithm for grayscale text document images. The algorithm inserts the watermark signals through edge direction histograms. The concept of sub-image consistency is developed. The concept means the sub-images have similar-shaped edge direction histograms and it is shown to be valid over a wide range of document images. Algorithms to insert and detect watermark signals are proposed. The experiments performed with various document images produced plausible results in terms of robustness. 2004 Elsevier B.V. All rights reserved.