A fragile watermarking scheme for authenticating images based on the Yeung-Mintzer scheme is proposed in this paper. This scheme does provide a better protection against all the attacks proposed for Yeung-Mintzer scheme. A polar set derived from the image blocks is used in the embedding process. The center pixel values of image blocks are perturbed by small quantities in such a way that the perceptual quality of the image is not modified. This paper also analyse the security level with respect to other attacks.