1. An image processing apparatus comprising: subject type-by-type certainty calculating means for calculating certainties representing to what degrees of confidence respective ones of images representing a predetermined plurality of subject types are contained in an image represented by applied image data, the calculation being performed for every prescribed subject type based upon a feature value obtained from the image data; subject type-by-type correction value calculating means for calculating correction values regarding respective ones of the plurality of subject types based upon the image data; correction-value unifying means for calculating a unified correction value obtained by weighting each of the correction values, which have been calculated by said subject type-by-type correction value calculating means, with regard to corresponding subject types by weights conforming to the subject type-by-type certainties calculated with regard to respective ones of the plurality of subject types by said subject type-by-type certainty calculating means, and unifying the subject type-by-type values obtained by weighting; image data correction means for correcting the image data using the unified correction value calculated by said correction-value unifying means; and further comprising subject-type designating means; wherein said subject type-by-type certainty calculating means calculates the subject type-by-type certainty with regard to a subject type designated by said subject-type designating means or a subject type other than a subject type designated by said subject-type designating means; and said subject type-by-type correction value calculating means calculates the subject type-by-type correction value with regard to a subject type designated by said subject-type designating means or a subject type other than a subject type designated by said subject-type designating means.