Subject indexing of textual materials such as books and journal articles is usually aided by the availability of several convenient sources of information--title, table of contents, abstract, or index--from which to determine the author's scope and purpose and the overall subject of the work. Several specific headings usually can be selected to describe the content of the book or article.
Picture indexers frequently have no such convenient sources. There may not be any written documentation accompanying the material by which to identify the "Who? What? Where? When? and Why?" of its creation and purpose. A cataloger may, therefore, have to invest some time in research in order to answer these questions before describing and indexing images.
The task of devising a title often falls to the cataloger as well, since many pictorial items and groups lack them; Graphic Materials offers guidance in devising descriptive titles. The information supplied in the title is usually expanded in a Summary Note (MARC field 520), which more fully outlines the subject of the images at hand, particularly for group-level records. Composition of the title and summary data are closely linked to assignment of subject terms, since all subject access points should be substantiated in the body of the descriptive cataloging record.
Catalogers should consider some additional questions when trying to decide which subjects to index. How historically significant is the subject matter of the images? Is the subject matter widely depicted, or are there novel aspects which are rarely found in pictorial collections? If a subject is not prominently or clearly shown in an image, can it be omitted in indexing because it is better represented elsewhere? How does the material relate to other collections in the institution? How can such significant relationships be highlighted through consistent description and indexing from one collection to the next? Does a group of images demonstrate that the creator had a particular point of view or message in mind, thus providing a rationale for indexing for the context as well as the content? It is often important to remember that the images being cataloged may, in fact, be unique primary evidence of a particular time and place.