Patent ID: 7343025

Claim:
A method of embedding a digital watermark on a wavelet lowest subband of an original image, the method comprising the steps of: wavelet transforming the original image into n levels; setting the wavelet lowest subband of the wavelet-transformed original image as a watermark embedment region; high-frequency filtering an original picture LL n of the watermark embedment region to generate a mirror picture LL n ′ from which a high frequency component of the original picture LL n has been eliminated; generating (i) index information designating a plurality of pixel positions within the watermark embedment region where the watermark is to be embedded, and (ii) a sequence of watermark values to be embedded in said pixel positions, respectively; calculating an embedment strength λ for each said pixel position of the watermark embedment region, considering a variance degree of an original picture LL n coefficient value; for each said pixel position, selectively altering the original picture LL n coefficient value based on (a) a corresponding mirror picture LL n ′ coefficient value, (b) the watermark value to be embedded in said pixel position, and (c) the embedment strength λ of said pixel position; and selectively embedding the watermark at each said pixel position with the selectively altered original picture LL n coefficient value while skipping watermark embedment where the original picture LL n coefficient value before and after said altering differs by more than a predetermined value associated with the corresponding embedment strength λ.