1. An image processing device for performing positioning processing on a plurality of images using a positional displacement amount between the plurality of images, the image processing device comprising: a measurement precision determination unit that determines a measurement precision, which is used when measuring a motion vector between the plurality of images, based on information indicating a distortion in an optical system; a motion vector measurement region setting unit that sets a plurality of motion vector measurement regions in which the motion vector is to be measured on an image; a motion vector calculation unit that determines the motion vector between the plurality of images in each of the plurality of motion vector measurement regions at the determined measurement precision; and a positional displacement amount calculation unit that determines the positional displacement amount between the plurality of images based on the motion vector determined in each of the plurality of motion vector measurement regions.