A watermarking scheme that varies the coefficient is described. A watermark element is embedded in the scheme, according to blocks. This scheme generates watermarked images with a desired objective image quality in terms of the peak signal-to-noise ratio, and it extracts an embedded watermark without any reference images. The proposed scheme can change the.subjective image quality of a watermarked image independent of the objective image quality by selecting the coefficient for embedding according to the blocks. However, malicious detection of the embedding coefficients becomes difficult.