Image indexing in the Bodleian ballads project

The creation of a digital database of broadside ballads at the Bodleian Library presents the challenge of cataloguing and indexing a large collection of documents containing both textual and visual material. The woodcut illustrations of the ballads will be indexed by subject using ICONCLASS, but it is not clear how this indexing should be integrated with that of the textual material. How does the cataloguing of images differ from the cataloguing of texts? And how successful is ICONCLASS in establishing communication between the indexer and the user?