1. An image processing apparatus comprising: setup means for setting up exposure values of a plurality of stages for image pickup means; extraction means for extracting the contour of an object in image signals output from the image pickup means; generation means for generating first histograms for image signals before extraction and second histograms for image signals after extraction for the respective stages with the broadening of the distribution in the histograms set constant; calculation means for calculating the amount of change between the kurtosis of the first histograms and the kurtosis of the second histograms for the respective stages; and selection means for selecting, of the image signals after the extraction corresponding to the respective stages, an image signal after the extraction corresponding to one of the stages in which the amount of change is larger than a predetermined amount as an optimum image for an object to be picked up.