A first value which is derived from a cluster belonging to an object appearing in an image (for example, the frequency with which said object appears among all objects of all images), and a second value indicating the features of the object in the image (for example, the relative size of the object to the image) are calculated. The degree of importance of one or more objects appearing in the image and the degree of importance of the image are calculated on the basis of the first value and second value.