Applications of the naturalness preserving transform to image watermarking and data hiding

The paper presents an image watermarking technique using the naturalness preserving transform (NPT). The goal is to produce an invisible and robust watermark that resists signal processing and geometric distortion attacks. Unlike traditional techniques, the proposed algorithm inserts and extracts the watermark via a special orthogonal transform class in between the spatial and frequency representations of the host image data. Two modified forms of the NPT employing the Hartley and discrete cosine transforms, respectively, are presented in order to improve the quality of the transformed image. Enhancements for the quality of the transformed images are achieved via reduction to the artifacts that occur to images transformed via the classical Hadamard-based NPT. The proposed watermark has demonstrated robustness against a variety of image attacks including, JPEG compression, low pass filtering, image cropping, and noise. The marked image must be severely degraded in order to prevent the reconstruction of the watermark. (C) 2004 Elsevier Inc. All rights reserved.