Abstract The widespread popularity of the Web has supported collaborative efforts to build large collections of community-contributed media. For example, social video-sharing communities like YouTube are incorporating ever-increasing amounts of user-contributed media, or photo-sharing communities like Flickr are managing a huge photographic database at a large scale. The variegated abundance of multimodal, user-generated material opens new and exciting research perspectives and contextually introduces novel challenges. This chapter reviews different collections of user-contributed media, such as YouTube, Flickr, and Wikipedia, by presenting the main features of their online social networking sites. Different research efforts related to community-contributed media collections are presented and discussed. The works described in this chapter aim to (a) improve the automatic understanding of this multimedia data and (b) enhance the document classification task and the user searching activity on media collections
