1. A method comprising: extracting, by at least one of the one or more computing devices, multimedia features from multimedia data items of a corpus of multimedia data items; arranging, by at least one of the one or more computing devices, the multimedia data items in clusters based at least in part on similarities of the multimedia features; calculating, by at least one of the one or more computing devices, at least two relevance features, including: first relevance features representing distribution characteristics of distances between pairs of multimedia data items in a same cluster; and second relevance features representing distribution characteristics of distances between different clusters of multimedia data items; and refining, by at least one of the one or more computing devices, the corpus by removing one or more multimedia data items from the corpus based in part on the at least two relevance values.