1. A user authentication method using a face image, comprising: (a) transforming a face image in a normalized spatial domain into frequency-domain data; (b) extracting valid transform coefficients from the frequency-domain data, based on energy-concentrated region information; (c) extracting a feature vector from the extracted valid transform coefficients; and (d) performing user authentication by comparing the extracted feature vector with a previously registered feature vector, wherein the energy-concentrated region information comprises information regarding an energy concentration region having the transform coefficients with a high degree of redundancy, the energy concentration region being extracted from an energy probability map of the face image; extracting a energy-concentrated region having transform coefficients that have a high degree of redundancy by using the energy probability map of the face images.