Abstract: With the emerging of high-resolution scanner and printer, the study of copyright protection for presswork becomes an important research realm. Based on analyzing the geometric and pixel value distortion of the image scanned from legal and pirated versions of presswork respectively, we propose a digital semi-fragile watermark based copyright protection method. The method first embeds watermark into the geometric invariant Fourier-Mellin domain of an image to weaken the geometric distortion, brought by printing process, of the watermark in presswork, and the image is then used to create presswork via a legal printing process. Secondly, the method rectifies rescanned image from the presswork by using Radon transformation and the embedded watermark in it is detected. Since there is an obvious difference between the destruction degrees of the watermark caused respectively by legal and pirated printing process, we can judge whether a copy of presswork is valid or not just by computing the ratio of the successfully derived watermark and comparing it with a predefined threshold. The experiments show that our method overcomes the shortcoming of the existing algorithms and can be used in copyright protection of various presswork.