Original Unmarked Image Research Articles

Quantization-Based Image Watermarking by Using a Normalization Scheme in the Wavelet Domain

To improve the invisibility and robustness of quantization-based image watermarking algorithms, we developed an improved quantization image watermarking method based on the wavelet transform and normalization strategy used in this study. In the process of watermark encoding, the sorting strategy of wavelet coefficients is used to calculate the quantization step size. Its robustness lies in the normalization-based watermark embedding and the control of its amount of modification on each wavelet coefficient by utilizing the proper quantization parameter in a high entropy image region. In watermark detection, the original unmarked image is not required, and the probability of false alarms and the probability of detection are discussed through experimental simulation. Experimental results show the effectiveness of the proposed watermarking. Furthermore, the proposed method has stronger robustness than the alternative quantization-based watermarking algorithm.

Wavelet-based oblivious image watermarking scheme using genetic algorithm

In this work, a robust and oblivious image watermarking scheme based on discrete wavelet transform (DWT) for copyright protection is presented. The original unmarked image is not required for watermark extraction. Third-level DWT is applied to the original cover image. Third- and second-level horizontal detail sub-band (LH2 and LH3) coefficients are grouped into different blocks. Grouping of the coefficients is done in such a way that each block should contain one coefficient from LH3 sub-band and four coefficients from LH2 sub-band. In each block, the first minimum and the second minimum are identified and modified according to the watermark bit. After watermark insertion, inverse DWT is applied to the sub-bands with modified coefficients to obtain the watermarked image. For watermark extraction, a threshold-based decoder is designed. Embedding and extraction process are characterised with parameters and genetic algorithm is used for parameter optimisation. Optimisation is to maximise the values of peak signal-to-noise ratio of the watermarked image and normalised cross correlation of the extracted watermark. The performance of the proposed scheme is compared with the existing schemes and significant improvement is observed. Experimental results show that, this algorithm is highly robust for many image attacks on the watermarked image.

Hiding iris data for authentication of digital images using wavelet theory

This paper introduces an efficient approach to protect the ownership by hiding an iris data into digital image for an authentication purpose. It is based on the theory of wavelets. The idea is to secretly embed biometric data (iris print) in the content of the image identifying the owner. The system is based on an empirical analysis of biometric and watermarking technologies, and it is split into several processes. The first process is based on iris image analysis, which aids the generation of the iris code (watermark); the second and the third processes deal with embedding and detecting a watermark; and the last process deals with the authentication. A new metric that measures the objective quality of the image based on the detected watermark bit is introduced, which does not require the original unmarked image for watermark detection. Simulation results show the effectiveness and efficiency of the proposed approach.

A Copyright Protection using Watermarking Algorithm

In this paper, a digital watermarking algorithm for copyright protection based on the concept of embed digital watermark and modifying frequency coefficients in discrete wavelet transform (DWT) domain is presented. We embed the watermark into the detail wavelet coefficients of the original image with the use of a key. This key is randomly generated and is used to select the exact locations in the wavelet domain in which to embed the watermark. The corresponding watermark detection algorithm is presented. A new metric that measure the objective quality of the image based on the detected watermark bit is introduced, which the original unmarked image is not required for watermark extraction. The performance of the proposed watermarking algorithm is robust to variety of signal distortions, such a JPEG, image cropping, geometric transformations and noises.

A geometrical transformations resistant digital watermarking based on quantization

A geometrical transformations resistant digital image watermarking based on quantization is described. Taking advantage of the rotation, scale and translation invariants of discrete Fourier transform (DFT), each watermark bit is embedded into each homocentric circles around the zero frequency term in DFT domain by quantizing the magnitude vector of Fourier spectrum. The embedded sequence can be extracted by “majority principles” without restoring to the original unmarked image. The experimental results show that the watermark is invisible and robust to any combination of geometrical transformations or common image processing techniques.

Automatic recovery of invisible image watermarks from geometrically distorted images

One method of attacking an imbedded invisible watermark is to create a derivative image that is geometrically distorted relative to the original. One attack, developed at Cambridge University, is called ‘‘StirMark.’’ 1 Image-distorting methods modify images so subtly that the changes are essentially unnoticeable to a viewer. However, their effect on invisible watermarks can be devastating, rendering them unextractable. In this paper, an automated countermeasure to image-distorting attacks will be described. Employing an unmarked copy of the original image as a reference, the possible distortion in a suspect image is first detected by the method, then measured, and finally reversed, producing a restored image approximately geometrically aligned with the original. Using a robust invisible watermarking method described previously by one of the authors to produce a watermarked image, ‘‘StirMark’’ to distort the watermarked image, and a copy of the original unmarked image for reference, the restoration method is demonstrated to be sufficient by showing successful extraction of the imbedded watermark from a restored image.

Copyright protection of digital images by embedded unperceivable marks

Digital watermarking has been proposed as a solution to the problem of copyright protection of multimedia documents in a networked environment. It makes it possible to tightly associate a code to an image, allowing the identification of the data creator, owner and so on. In this paper, after a review of some important watermarking techniques, a new watermarking algorithm for digital images is presented: the method, which enhances a previous technique proposed by Cox et al. [1] [I.J. Cox, J. Kilian, T. Leighton, T. Shamoon, Secure spread spectrum watermarking for multimedia, NEC Research Institute Technical Report 95-10], operates in the frequency domain, by embedding in a selected set of DCT coefficients a sequence of randomly generated real numbers. By exploiting their statistical characteristics, it is possible to reliably extract the embedded sequences without resorting to the original unmarked image. Experimental results demonstrate that the watermark is robust to several image transformations.