It's important and necessary to detect and prove the ownership of a digital work in the communication technology era. The purpose of this paper is to propose a digital watermarking scheme for images. In this scheme, first, a watermark signal is produced by a chaotic sequence. Then the watermark is placed in the cosine transform coefficients of a host image. Next, the watermarked image is exposed to some attacks such as filtering, compression, rotation and addition of noise. The simulation results show the ability of the proposed method in maintaining the watermark after conducting these attacks. In the following, in addition to comparing the propose method with other similar methods, the superiority of this scheme over other methods will be remarkable and confirm able. In the following, in addition to comparing the propose method with other similar methods, the superiority of this scheme over other methods will be remarkable and confirm able. پرونده مقاله