Visual secret sharing watermarking for digital image

A visual secret sharing watermarking (VSSW) technique is proposed as a way of solving copyright protection problems for digital images. The proposed watermarking technique employs a visual secret sharing (VSS) scheme and separates the watermark into two parts, a public watermark and a secret watermark. For watermarking security, only the public watermark is inserted into the original image, while the owner holds the secret watermark. Without the secret watermark, it is almost impossible to extract the watermark even if the embedding algorithm is published. To meet requirements of robustness and imperceptibility, we modify DCT coefficients belonging to the middle frequency band to embed the public watermark. Importantly, the watermark can be retrieved from the watermarked image without resorting to the original image. Various experiments using the proposed watermarking method are presented to demonstrate robustness to tampering and a to variety of common image processing operations and geometric manipulations.