1. An image processing apparatus, comprising: an image input device configured to read an original image and to obtain image data from the original image by selecting one of plural types of image reading modes of the image input device; an image pre-processing mechanism configured to perform at least one pre-processing relative to the image data obtained by the image input device; an image pre-processing selecting mechanism configured to select at least one pre-processing according to the image reading mode selected by the image input device and to cause the image pre-processing mechanism to perform the selected at least one pre-processing; and an information extracting mechanism configured to extract specific information included in the image data subjected to the at least one pre-processing performed by the image pre-processing mechanism.