Captions are text that describes some other information; they are especially useful for describing nontext media objects (images, audio, video, and software). Captions are valuable metadata for managing multimedia, since they help users better understand and remember (McAninch, Austin, & Derks, 1992-1993) and permit better indexing of media. Captions are essential for effective data mining of multimedia data, since only a small amount of text in typical documents with multimedia—1.2% in a survey of random World Wide Web pages (Rowe, 2002)—describes the media objects. Thus standard Web browsers do poorly at finding media without knowledge of captions. Multimedia information is increasingly common in documents as computer technology improves in speed and ability to handle it, and people need multimedia for a variety of purposes like illustrating educational materials and preparing news stories. Captions are also valuable because nontext media rarely specify internally the creator, date, or spatial and temporal context, and cannot convey linguistic features like negation, tense, and indirect reference. Furthermore, experiments with users of multimediaretrieval systems show a wide range of needs (Sutcliffe, Hare, Doubleday, & Ryan, 1997), but a focus on media meaning rather than appearance (Armitage & Enser, 1997). This suggests that content analysis of media is unnecessary for many retrieval situations, which is fortunate, because it is often considerably slower and more unreliable than caption analysis. But using captions requires finding them and understanding them. Many captions are not clearly identified, and the mapping from captions to media objects is rarely easy. Nonetheless, the restricted semantics of media and captions can be exploited.
Collaborative multimedia systems: synthesis of media objects
