1. An image processing apparatus comprising: an auto continuous-capturing unit for continuously capturing a plurality of unit images; a feature point detecting unit for extracting and setting a feature point to be compared from each unit image; a motion detecting unit for detecting a feature point corresponding to the feature point of the unit image from another unit image in a feature point detection range; an image matching unit for reducing an error between the unit images by moving and modifying the unit image based on declination of the feature points; an image synthesizing unit for outputting a synthesized image by superposing the unit images; and a motion detection range calculating unit for calculating the feature point detection range according to a hand-shake limit pixel number, which is the maximum number of pixels allowing shake not to be substantially perceived in the unit image.