1. An image processing apparatus that generates one output image from plural input, images, the image processing apparatus comprising: detecting means for detecting a positional relation among the plural input images photographed by imaging means for photographing an image; pixel-value calculating means for calculating a pixel value of a pixel of the output image using pixel values of pixels of the input images and an interpolation function that changes according to positions of the pixels of the input images after positioning obtained by performing positioning of the plural input images on the basis of the positional relation; determining means for determining whether the pixel of the output image is a motion pixel that is a pixel in an area in which a moving subject appears; and adjusting means for adjusting a high-pass characteristic of the interpolation function on the basis of a result of the determination on whether the pixel of the output image is a motion pixel.