A DWT based Dual Image Watermarking Technique for Authenticity and Watermark Protection

In this paper we propose a DWT based dual watermarking technique wherein both blind and non-blind algorithms are used for the copyright protection of the cover/host image and the watermark respectively. We use the concept of embedding two watermarks into the cover image by actually embedding only one, to authenticate the source image and protect the watermark simultaneously. Here the DWT coefficients of the primary watermark (logo) are modified using another smaller secondary binary image (sign) and the midfrequency coefficients of the cover/host image. Since the watermark has some features of host image embedded in it, the security is increased two-fold and it also protects the watermark from any misuse or copy attack. For this purpose a new pseudorandom generator based on the mathematical constant π has been developed and used successfully in various stages of the algorithm. We have also proposed a new approach of applying pseudo-randomness in selecting the watermark pixel values for embedding in the cover image. In all the existing techniques the randomness is incorporated in selecting the location to embed the watermark. This makes the embedding process more unpredictable. The cover image which is watermarked with the signed-logo is subjected to various attacks like cropping, rotation, JPEG compression, scaling and noising. From the results it has been found that it is very robust and has good invisibility as well.