Digital image watermarking in spatial and transform domains

This paper reviews both spatial and frequency domain watermark embedding schemes for single-frame images. It focuses on the application of quantum distributed private keys in the concealment of data in images. Simple examples are used to illustrate the approach. In the spatial domain, differential PCM is used to detect the edge regions of the image so that data can be hidden on those pixels of the image when the differential signal is larger than a certain threshold level. The method is based on the visual masking phenomenon at large intensity transitions in the neighbourhood of the pixel. In the frequency domain, DCT coefficients with significant variance are chosen and modulated using the private key sequence. Both spatial and DCT schemes are evaluated in terms of the peak signal-to-noise ratio (PSNR).