1. An image processing apparatus, comprising: an area setting section that sets a searching area of a predetermined size in inputted image data; a searching section that searches for pixels having a predetermined pixel value in the searching area set by the area setting section; an attribute determining section that determines attribute of pixels contained in the searching area on the basis of at least either of a number and an arrangement of the pixels searched for by the searching section; and an attribute assigning section that assigns the attribute determined by the attribute determining section to the searched pixels.