1. A method for creating a face replacement database, comprising: creating a face database for storing a plurality of replacement face images, each replacement face image having a rotation angle determined according to a method for estimating a 3-D vector angle from a 2-D face image, and defining a target replacing region in each replacement face image, wherein the method for estimating a 3-D vector angle from a 2-D face image includes: creating a feature vector template including a feature vector model of a plurality of different rotation angles, detecting a corner of each of two eyes and two corners of a mouth in a face image to be processed, defining the corners of the eyes and the two corners of the mouth as respective vertices of a quadrilateral, defining a sharp point displaced in an orthogonal direction relative to the quadrilateral plane, converting the vertices into 3-D coordinates, wherein the sharp point and the vertices of the quadrilateral form a quadrangular pyramid, computing four 3-D vectors, each 3-D vector extending from the sharp point to a respective one of the four vertices of the quadrilateral, wherein the coordinates of said 3-D vectors are 3-D coordinates, and wherein said 3-D vectors are computed to obtain a vector set, matching the vector set with the feature vector model to obtain an angle which has the shortest distance between a feature vector model and the vector set, and defining the obtained angle value as a rotation angle of the input face image.