1. A representative image display device that selects representative images according to grouping results of a plurality of images and sub-clusters and displays the selected representative images on a display, the images being grouped into the sub-clusters such that each sub-cluster includes similar images, the sub-clusters being grouped into a plurality of clusters such that each cluster includes similar sub-clusters, the representative image display device comprising: a cluster selection unit operable to select one or more of the clusters as representative clusters; a sub-cluster selection unit operable to select, from each representative cluster, M sub-clusters as representative sub-clusters based on first likelihoods of the sub-clusters in the representative cluster, each first likelihood indicating accuracy of the grouping result of the corresponding sub-cluster (M is an integer satisfying a relationship 1≦M≦the number of the sub-clusters in the representative cluster); and a representative image selection unit operable to select, from each representative sub-cluster, N images as representative images based on second likelihoods of the images in the representative sub-cluster, each second likelihood indicating accuracy of the grouping result of the corresponding image (N is an integer satisfying a relationship 1≦N≦the number of the images in the representative sub-cluster), wherein the sub-cluster selection unit (i) selects, from each representative cluster, the sub-cluster having a highest first likelihood in the representative cluster as a first representative sub-cluster, and (ii) when M is greater than or equal to 2, further selects, from each representative cluster, (M−1) sub-clusters as second to M th representative sub-clusters in order of a lowest first likelihood, and wherein the sub-cluster selection unit uses, as the first likelihood of each sub-cluster, a distance between (i) a central position or a center of mass of a feature space of the corresponding representative cluster and (ii) a central position or a center of mass of a feature space of the sub-cluster.