Resistant image watermarking in the phases of the Complex Hadamard Transform coefficients

In the paper a new method is presented for digital content protection based on watermark data insertion in the image transform domain. For this, the still digital image is transformed using Complex Hadamard Transform (CHT), and the watermark data is then inserted in the imaginary part of the transform coefficients. The selection of the suitable for watermarking transform coefficients is done in accordance with pre-defined rules. The so inserted watermark is perceptually invisible. The method permits the insertion of relatively large amount of data, retaining the high quality of the protected image. The main advantages of the algorithm for digital watermarking, based on the CHT are that it is resistant against attacks, based on high-frequency filtration (JPEG compression); it permits the insertion of significant amount of data, and the watermark detection could be done without using the original image.