1. An image processing method comprising: calculating a first index value utilizing back matching between a first image and a second image in relation to a first pixel which is one or a plurality of pixels of the first image and a second pixel which is one or a plurality of pixels located at a position corresponding to the first pixel in the second image; calculating a second index value by normalizing a correlation index value indicating correlation between the first pixel and the second pixel using a complexity index value indicating complexity of an image which is displayed by the first pixel; and calculating a third index value by multiplying the first index value by the second index value.