1. An image processing apparatus comprising: an image detector having a plurality of pixels and configured to convert an optical image into an image signal to pick up the image signal as an image; a moving unit configured to move the image detector from a first position by a distance greater than or equal to a pixel width; a control unit configured to control the image detector and the moving unit such that a first image is picked up by the image detector at the first position, and that a second image is picked up by the image detector at a second position displaced from the first position by the distance greater than or equal to the pixel width; and a combining unit configured to combine the first image and the second image to form a composite image by changing, in coordinates of the composite image, coordinates of the second image to values corresponding to the distance.