1. A learning device comprising: feature point extracting means configured to extract a feature point from each of a plurality of images for generation to be used for generating an identifier for identifying whether or not a subject existing on an image is a predetermined object to be identified, which are made up of a positive image where said object to be identified exists, and a negative image where said object to be identified does not exist; feature point feature amount extracting means configured to extract feature point feature amount representing the feature of said feature point from said image for generation; whole feature amount calculating means configured to calculate the whole feature amount representing the feature of the whole of said image for generation from said feature point feature amount of said image for generation based on a shared code book including feature amount for generation to be commonly used for generation of an identifier for identifying each of different objects to be identified; and identifier generating means configured to generate said identifier based on said whole feature amount of said image for generation, and a correct answer label representing whether said image for generation is said positive image or said negative image.