1. A teaching data setting apparatus for setting teaching data required for image processing associated with mounting electronics, comprising: a subject teaching data generating section that stores in advance subject attributes related to a subject to be mounted and recognition operation conditions required for the image processing, and generates a plurality of pieces of teaching data representing all possible combinations of the subject attributes and the recognition operation conditions; a teaching data candidate selecting section that selects, from the plurality of pieces of teaching data generated by the subject teaching data generating section, teaching data candidates related to the subject and a mounting machine for use; a subject image input section that is supplied with a simple subject image representing only the subject; an evaluation image generating section that generates a predetermined evaluation image required for determining optimum teaching data for the subject by using the simple subject image supplied to the subject image input section; and a teaching data determining section that determines, based on the evaluation image generated by the evaluation image generating section, a piece of teaching data as the optimum teaching data for the subject out of the teaching data candidates selected by the teaching data candidate selecting section.