A watermark is embedded in spatial domain. However, the same effect as the watermark is embedded in frequency domain is obtained by inverse frequency transforming the watermark, and then embedding it. By doing that, robustness of the watermark is enhanced in comparison with conventional method for generating a watermark and adding it in spatial domain. Also, the watermark can be detected, even though an image is passed through stirmark, by enlarging the size of the watermark generated by inverse frequency transforming through re-sampling.In detecting the watermark, by high frequency filtering the watermarked image and getting all blocks of the watermarked image together, the effect of removing image component is obtained. Thereby, the detection speed of the watermark is improved, and the detection rate is increased as well.