1. An image processing method for recognizing one or more quadrangles from an input image, the method comprising the steps of: (a) detecting a plurality of edge areas from the input image; (b) extracting a plurality of lines; the lines corresponding to the edge areas detected; (c) categorizing a line pair selected from the extracted lines according to a positional relationship between two lines included in the line pair, and calculating a line pair evaluation value for the line pair; (d) selecting a combination of two line pairs from a plurality of line pairs, generating a quadrangle from four lines included in the two line pairs selected, and calculating a quadrangle evaluation value for the quadrangle based on the categories and the line pair evaluation values of the two line pairs forming the quadrangle; and (e) selecting a quadrangle based on the calculated quadrangle evaluation value.