The anti-counterfeiting watermarked images of lithographic prints must be transformed into digital images by
scanner or camera before authenticating. The obtained images usually happen to geometric distortion so as to influence
the watermark extraction. A geometric distortion correction method for the lithographic watermarked authentication
images is proposed in this paper. Hough transform is used to detect the edge lines or corner points, and then unites with
the nature of the oblique distortion or the perspective transformation model to correct the distortion. Finally,
morphological filtering is used to revise the corrected images. Experiments results demonstrate the method can correct
the geometric distortion well and the watermarking image can be extracted and clear enough to authentication.