1. An image evaluation apparatus for evaluating each of a plurality of images, the images including objects that each belong to a cluster, the image evaluation apparatus comprising: a first value calculating unit that calculates a first value pertaining to an object appearing in an image, of the plurality of images, according to a cluster that the object belongs to; a second value calculating unit that calculates a second value indicating a degree of appearance of the object in the image; and an evaluating unit that calculates, according to the first value and the second value, an object importance degree and an image importance degree, wherein the evaluating unit (i) creates a graph including a link between the image and the object, the link indicating a relationship between the image and the object, and (ii) when a first object and a second object appear together in the image, calculates, by using the graph, the object importance degree for each of the first and second objects such that importance propagates from one of the first and second objects to another of the first and second objects, the evaluating unit includes: an object importance degree calculating unit that calculates the object importance degree according to the first value and the second value; and an image importance degree calculating unit that calculates the image importance degree according to the object importance degree calculated by the object importance degree calculating unit, the first value calculating unit calculates a frequency degree as the first value, the frequency degree indicating a frequency at which one or more objects, belonging to a same cluster as the object, appear in the plurality of images, the second value calculating unit calculates an occupation degree as the second value, the occupation degree indicating a proportion of an area of the image that is occupied by the object, and the object importance degree calculating unit uses the frequency degree and the occupation degree in order to calculate the object importance degree.