An information loss determiner in an image processing device determines whether character collapse has occurred in a simple binarized image. If character collapse has not occurred in the simple binarized image, an image processing determiner selects simple binarization processing as the image processing method of output image data. If character collapse has occurred in the simple binarized image, the process proceeds to photograph area size determination. If the ratio of a photograph area size is less than or equal to a predetermined value, the information loss determiner determines that character collapse has occurred in a posterization processed image. If character collapse has occurred in the posterization processed image, the image processing determiner selects grayscale processing. If character collapse has not occurred in the posterization processed image, the image processing determiner selects posterization processing.