1. An image processing apparatus comprising: a characteristic region detecting section that detects a characteristic region from an input image; an image generating section that generates, from the input image, a low-quality image which is of lower quality than the input image, and a characteristic region image which is of higher quality than the low-quality image at least the characteristic region, the low-quality image having decreased resolution; a difference processing section that generates a characteristic region difference image indicating a difference between an image of the characteristic region in the characteristic region image and an enlarged image of the characteristic region in the low-quality image; and an encoding section that encodes the characteristic region difference image and the low-quality image; wherein the difference processing section generates the characteristic region difference image having a spatial frequency component in the characteristic region and a spatial frequency component with a decreased data amount in a region other than the characteristic region, the spatial frequency component being obtained by converting the difference between the enlarged image and the characteristic region image into a spatial frequency domain.