A new invisible color image watermarking framework through alpha channel

In recent day image ownership authentication has drawn a sharp attention due to easy availability of the internet and inexpensive digital recording and storage peripherals has created an environment where duplication, unauthorized use, and maldistribution of the digital content has become easier that leads cyber crime. In aforesaid regard we´ve already proposed different fragile color image watermarking frameworks for embedding a color watermark within a color host image. The host image is simply divided into some blocks so that as per our proposed technique we are able to embed watermark at two LSBs in alpha channel of all such blocks. Although alpha channel is used for controlling the transparency of the image, but two LSB´s in the alpha channel are unused bits. In this scheme we have used these two bits for embedding information. They do not have any contribution in luminance and chrominance factor. For that reason watermark is fully invisible to the Human Visual System and no bits are changed in the red, green, and blue channel of the host image and for that reason no color information of the host image have been lost. So the color density of the original and watermarked image is same. In proposed watermarking framework, it allows a user with an appropriate secret key and a hash function to verify the authencity, integrity and ownership of an image. If a forger performs the watermark extraction with an incorrect key and inappropriate hash function, the user obtains an image that resembles noise. In this manner we are providing an integrated solution for ownership authentication where the watermark is unique for that particular host image, thus the authentication is ensured in an efficient way. At the watermark extraction end, we´ve used blind extraction method, i.e., neither the host image nor the watermark image is required at the time of watermark extraction.