Embedding parametric digital signatures in images

A new approach to digital image signatures (watermarks) is proposed in this study. An image signature algorithm consists of two stages : signature casting and signature detection. In the first stage, small changes are embedded in the image which afterwards are identified in the second stage. After chosing certain pixel blocks from the image, a constraint is embedded among their Discrete Cosine Transform (DCT) coefficients. Two different embedding rules are proposed. The first one employs a linear type constraint among the selected DCT coefficients and the second assigns circular detection regions, similar to the vector quantization techniques. The resistance of the digital signature to JPEG compression and to filtering are analyzed.