Subject heading options
Within your repository, depending on the software used, you would have the choice to enter either uncontrolled or controlled keywords within an item record. Although the addition of any type of keyword would enhance the item record, for consistency between all of the items in your collection and to benefit user searches, it may be best to again use a controlled vocabulary.
Set options for controlled dc:subject fields, or 'keywords,' within your repository may include Library of Congress (LC) Classification, Dewey Decimal Classification, or LC Authority Headings. However, you also may find it useful to use a standard specifically devised for art objects such as the AAT for describing the items within your collection. Another authority list that may also be useful is ULAN (Union List of Artists Names).