1. An image processing method in an image processing apparatus that performs image processing of images read by an image reader, the method comprising: an inputting step of inputting into the image processing apparatus an image signal corresponding to an entire image read by the image reader; a region-selecting step of selecting a region of the entire image read by the image reader; a first detecting step of detecting a first plurality of background-color candidates included in the entire image read by the image reader, based on a frequency distribution of the image signal corresponding to the entire image read by the image reader and input by the inputting step; a first calculating step of calculating a first area ratio of the first plurality of background-color candidates detected by the first detecting step; a second detecting step of detecting a second plurality of background-color candidates included in the selected region, based on a frequency distribution of an image signal corresponding to the selected region selected by the region-selecting step; a second calculating step of calculating a second area ratio of the second plurality of background-color candidates detected by the second detecting step; a third detecting step of detecting a background-color region in accordance with a first score obtained by scoring the first area ratio of the first plurality of background-color candidates included in the entire image and a second score obtained by scoring the second area ratio of the second plurality of background-color candidates included in the selected region; and a background-color-removing step of removing a background color contained in the selected region in accordance with a level of an image signal of the background-color region detected by the third detecting step.