Secure Spread Spectrum Based Multiple Watermarking Technique for Medical Images

Abstract

In this chapter, the authors presents a new spread-spectrum based secure multiple watermarking (image and text) method for medical images in wavelet transform domain. The proposed method is applied for embedding patient identity reference as text watermark and telemedicine centre logo as the image watermark into the host medical image. The algorithm is based on secure spread-spectrum technique where pseudo-noise (PN) sequences are generated corresponding to each watermark bit of the image watermark. These PN sequences are embedded column wise into the selected wavelet coefficients in the DWT sub-band. The selection of the wavelet coefficients for embedding is performed by thresholding the coefficient values present in that column. In order to enhance the robustness of text watermarks, an error correcting code (ECC) is applied to the ASCII representation of the text watermark before embedding. The results are obtained by varying the gain factor, sub-band decomposition levels, size of watermark, and different cover images. The performance of the proposed watermarking method is analyzed against known attacks. The method was found to be robust against such attacks. Further, the performance of the proposed method has been extensively evaluated for the text watermark along with BCH code and encryption techniques. The performance of the methods are compared with other reported techniques and have been found to be giving superior performance in terms of robustness, imperceptibility, embedding capacity and security as suggested by other authors. Moreover, the performance of the multiple watermarking method is also tested with encryption and BCH error correction code simultaneously.