1. A case image registration apparatus comprising: a determination unit including at least one processor which compares case information corresponding to an object image, which is a case image to be determined whether registration to a database is required or not, and an amount of feature of the object image, with case information corresponding to a registered image, which is a case image other than the object image and has been registered in the database, and an amount of feature of the registered image, and determines whether to register the object image in the database or not according to a result of the comparison; a registration unit which registers the object image when the determination unit determines to register the object image in the database; and further comprising a degree of similarity calculation unit which calculates a degree of similarity between the amount of feature of the object image and the amount of feature of the registered image, wherein the determination unit determines whether to store the object image in the database or not according to the comparison of the degree of similarity with a prescribed registered determination threshold, an item determination unit which collates the case information corresponding to the object image and the case information corresponding to the registered image with each other on an item by item basis, and determines whether the number of matching items in the collation exceeds a prescribed number threshold or not, wherein the degree of similarity calculation unit, when the item determination unit determines that the number of matching items having exceeds the prescribed number threshold, calculates the degree of similarity between the amount of feature of the object image and the amount of feature of the registered image, and wherein the item of the case information includes at least any one of: information pertaining to a patient including the name, sex, age and other information of the patient; information pertaining to imaging including a type of an imaging apparatus, an imaging condition and other information; information pertaining to diagnosis including a finding, a disease name and other information; a lesion position; and an anatomic position of the lesion position.