Hierarchical watermarking depending on local constraints

We propose a new watermarking technique where the watermark is embedded according to two keys. The first key is used to embed a code bit in a block of pixels. The second is used to generate the whole sequence of code bits The watermark is embedded in spatial domain by adding or subtracting a random digital pattern to the given image signal. The embedding depth level depends on the spectral density distribution of the DCT coefficients and on the JPEG quantization table. The label consists of a set of bits which are embedded locally in a rectangular set of blocks and it is repeated over the entire image. After detecting individual bits, the retrieved label is verified by performing a XOR operation to the watermark code.