1. An image processing apparatus, comprising: a selecting unit configured to select one image as a first image from images, and configured to define the other images as second images; a projective transformation unit configured to generate a projected depth map of a second image from a depth map of the first image, the depth map indicating a depth value of a pixel of a corresponding image; a subtracting unit configured to create a difference map of the second image, the difference map being a difference between a depth map of the second image and the projected depth map of the second image; and a storage unit configured to store the depth map of the first image and the difference map of the second image.