1. An image processing apparatus comprising: a characteristic obtaining unit configured to obtain a characteristic of a subject which is an original learning sample in an input subject image; a selection unit configured to select a type of image process which is associated with the obtained characteristic of the subject, where different types of image processes are associated with respective characteristics in advance; an image processing unit configured to generate a group of the subject images as additional learning samples by performing the selected type of image process on the subject image with different parameters; and a learning unit configured to learn a matching dictionary by using the original learning sample and the additional learning samples.