A technology for recognizing one or more quadrangles from an input image is disclosed. Edge areas are detected from the input image, lines corresponding to the edge areas are extracted, a line pair selected from the extracted lines is categorized according to a positional relationship between two lines included in the line pair, a line pair evaluation value is calculated for the line pair, a combination of two line pairs is selected, a quadrangle is generated from four lines included in the two line pairs selected, a quadrangle evaluation value is calculated for the quadrangle based on the categories and the line pair evaluation values of the two line pairs forming the quadrangle, and a quadrangle is selected based on the calculated quadrangle evaluation value.