Perceptible Content Retrieval in DCT Domain and Semi-Fragile Watermarking Technique for Perceptible Content Authentication

Digital watermarking was commenced to copyright protection and ownership verification of multimedia data. However the evolution of the watermark focused on different security aspects of multimedia data such as integrity and authenticity. Fragile and semi-fragile watermarking schemes were introduced to accomplish these requirements. In this paper, we propose semi-fragile watermarking scheme to authenticate visual content of the image. The proposed method is carried out in DCT domain and authenticating the particular number of low frequency coefficient, it achieves the integrity of the image. Since low frequency coefficients carry the essence of the visual data, authenticating only the low frequency data is adequate. Therefore the proposed technique is efficient than the others, which are processing in all DCT coefficients. Digital signature is generated by following the definition of elliptic curve digital signature algorithm (ECDSA). Thus, the scheme is faster than RSA based authentication definition and it provides high level of security and availability. Additionally our scheme localizes the compromised area of the image. Embedded and visual data are protected from quantization of JPEG by altering the quantization table. However the degradation of compression ratio due to alternation in quantization table has been evaluated. Experimental results show that the watermark does not make any visual artifact in original data and it gives evidence that compression ratio degradation is ignorable for average JPEG quality factors. Key-Words: semi-fragile watermarking, public key cryptography, discrete cosine transformation, image authentication, imperceptibility, elliptic curve digital signature algorithm, JPEG.