Abstract: Owing to personal computers being applied in many fields and Internet becoming popular and easier to use, most information is transmitted with digital format. Therefore, data copying and back up are more and more easier in the world wide web and multimedia. The copyright and authentication gradually lose their security. How to protect intellectual property becomes important in technical study and research. Recently, the watermarking technique was proposed to solve the problem of protecting the intellectual property. In this paper, a watermark embedded in the host image by DCT transform has been proposed. There are several papers using the same manner to embed watermark into middle-band coefficients of DCT block. The Joint Photograph Expert Group

(JPEG) image compression usually discards the high-band frequency in DCT block including some middle-band data. In this paper the lower-band coefficient of DCT block was employed, since it is robust against the attack by the JPEG. In order to improve the imperceptions, only one bit was embedded in each coefficient of a DCT block. The experimental results show the proposed approach is correct.

Keywords: Discrete Cosine Transform (DCT), Frequency Domain, Joint Photographic Experts Group (JPEG), Robust, Transparency.