A for embedding a digital watermark on a wavelet lowest subband includes: setting a DC component region of a multi-stage wavelet-transformed original copy image to a watermark embedment region, and high-frequency filtering an original picture LL.sub.n of the embedment region; generating index information for designating a pixel position, and a watermark sequence to be embedded; calculating an embedment strength .lamda. for each position of the watermark embedment region; in case the watermark sequence is sequentially embedded on an embedded position designated by the index information, mutually comparing the original picture LL.sub.n coefficient value for each embedded position with a mirror picture LL.sub.n' coefficient value, and then altering the original picture LL.sub.n coefficient value; and in case the original picture LL.sub.n coefficient value is differentiated above a predetermined value with reference to the coffesponding embedment strength .lamda., skipping the watermark embedment for the position.