In the field of the personal authentication system, types of hands are popularly used to certificate the identity of a person. There is an important part in the hand-shape recognition system. That is how to take the photographs of hands. Whether you use a camera or a scanner to take a photograph, there exist some shadow parts around a hand image. As for this part, to judge whether the shadow is true or it is just the hand plays an important role to improve the recognition rate. Actually if we can judge the range of the shadow of the hand image clearly we can raise the probability of the certification. In this paper we focus on the shadow part of hand images. We propose some algorithm to convert an original image into a better image to handle the hand-shape. Firstly, we make the convert the input color image into a grayscale image, then we extract the outline by using Fourier transform, and the true outline of the hand will be determined. Now the recognition methods using biometrics are spread in the world, we believe our project of processing the shadow part will be useful to the recognition system.