A novel design of a DFT-based digital watermarking system for images is proposed in this paper. The system provides images copyright protection which can be done by adding invisible watermark into the digital image. First, the original image is decomposed into DFT coefficients using a fast Fourier transform. For minimal loss in image fidelity, the watermark is embedded in those DFT coefficients with highest magnitudes except for those in the lowest one. The watermark detection is achieved without use of the original image by computing a similarity measure between the input watermark and the DFT coefficients of the attack image. Experimental results show that the proposed method is robust against the common image/signal processing operations. © 2006 IEEE.