1. An image processing apparatus comprising: first setting means for setting, for an original image, a first image region including a reference point arbitrarily selected on a screen thereof, and a second image region other than the first image region on the screen; reducing means for reducing the original image by decimating pixels of image data thereof; second setting means for setting, for a reduced image obtained by the reducing means, a reference point of the reduced image corresponding to the reference point of the original image, a first reduced image region corresponding to the first image region, and a second reduced image region corresponding to the second image region; modifying means for modifying, within the reduced image obtained by the reducing means, an image in the second reduced image region set by the second setting means so that the degree of modification increases with increasing distance from the reference point of the reduced image; expanding means for expanding image data of the second reduced image region, of which the image has been modified by the modifying means, into the second image region by interpolating pixel values between individual pixels constituting the image data; and combining means for combining the image data expanded into the second image region by the expanding means with image data of the original image constituting the first image region, and outputting image data of an image that is modified so that the degree of modification increases with increasing distance from the reference point of the original image.