A Study on Object Image Watermarking and Palette Image Steganography

論文名稱: A Study on Object Image Watermarking and Palette Image Steganography
物件影像浮水印與調色盤影像資料隱藏技術之研究


The current rapid development of information technologies makes provision of commercial multimedia services on Internet. However, in rerum natura, digital multimedia is easy to be copied, re-scaled, rotated, transformed, and modified using handy processing software without much effort. This fact has derived an urgent demand for reliable and secure copyright protection for digital multimedia. Watermarking is the technology used for copy control and media identification and tracing. Most proposed watermarking methods are designed for the protection of digital images. Theses methods embed a short message (a watermark) in the image without affecting the usability but that can be detected using dedicated analysis software.
Watermarking techniques have been widely discussed and developed in recent years. However, studies which focus on watermarking techniques those can resist geometrical attacks are still not quite mature. Geometrical attacks like rotation, scaling, and transforming will miss-position the location of watermark embedded. There are some previous works working on this problem for watermark re-synchronization. We use the geometrical features of object shape in a digital image to achieve the goal of watermark re-synchronization to obtain quite remarkable imperceptibility and robustness.

In this dissertation, we aim to design some information hiding techniques for protecting images and private messages of communication on the Internet. Four information hiding related schemes are proposed. They are (1) Geometric attack free self-synchronized object image watermarking schemes (2) Palette-based object image watermarking scheme (3) Palette-based image Steganography scheme, and (4) Hierarchic texture classification based on statistical steganography.
First of all, to achieve the goal of watermark re-synchronization and embed digital watermark into an object image, geometric features of an object image like the length of principal axes, eigenvectors, and orient of mass center are use for subdividing the object shape. Using those geometric features for shape subdividing makes re-synchronization of watermark detection possible. In our study, different shape subdivision methods, including self-similarity, parallel segmentation and recursively principal axes, are proposed for object watermark embedding. And the geometric attack resistance schemes for object images can be applied to different image formats, including raw and palette-based images. Unlike the true color images and gray level images, palette-based images have discrete color palette. To embed watermark into limited colors and hold the imperceptibleness and robustness is a challenging work. An algorithm for palette-based object image watermarking is proposed here. These proposed methods are easily implemented and can obtain comparable NC values to against outside geometrical attacks such as rotation, scaling and translation.
For the issue of steganography, an iterative method of palette-based image steganography scheme is proposed to improve the existed methods. Better quality of stego- images can be produced using the proposed method. Besides, we also proposed a hierarchic texture classification using statistical steganography technique to obtain robust texture features for texture classification. Experimental results show that the proposed methods can achieve high accuracy rate and also work well even the query textures are distorted by noise corruption or compressed.