In this paper, we propose a non-embedded watermarking based on a trusted third party, coefficients features of DCT and edge detection. The algorithm first calculates the edge information of the images by DCT coefficients and then computes authentication codes with the edge information. The non-embedded watermarking technology avoids the damage of the original image, which is caused by traditional watermarking. The experiments have shown that, compared with conventional DCT-based watermarking algorithm，the algorithm proposed in this paper is much more efficient in resisting general image processing operations (e.g. sharpening, noising, invert, etc), JPEG compression, and geometric attacks (e.g. rotation, cropping, etc).