of intensity shift linear filtering and additive noise in the frequency domain in particular the approximations involve modeling the modifications or degradations as an unknown change to the d c component multiplication by a smooth mask and additive noise a solution for ensuring the protection of digital images according to the present invention involves modifying an original digitized image i i j to produce another image i w i j that will include embedded information on the image source and its legal user the amount of information in the watermark is in the range between 30 to 100 bits with the following conditions applicable 1 the tags watermarks are imperceptible i e i w appear very similar to the original images i 3 tags are not easily identifiable from one or more differently tagged copies of the image 4 tags are easily recoverable from a tagged image and the original 5 attempts to remove the tags or tamper with them have noticeable ill effects on the image 6 tags cannot be wiped out by image modification compression algorithms or by other casual image processing procedures 7 tags are distributed in the image plane and are recoverable from u201c arbitrary u201d portions of the image i e they survive image cropping referring now to fig1 and in accordance with one embodiment of the present invention a watermark authentication system satisfying the criteria above and generally designated 30 includes a watermarking apparatus 40 for embedding a watermark into the frequency domain of a given image.