The service is part of a re-release by the Library of Congress of its Print & Photographs Online Catalog. It provides access to a rich image collection for incorporation into other applications. Applications can search the catalog by description term, and if desired within particular collections, for specific image types, etc. Results can include just descriptive metadata or the images themselves, presented as a list, grid, slideshow, or gallery.
API methods support specification of a search query, either across the entire collection or restricted to certain elements, along with optional filtering criteria like subject and format. Methods also enable structuring of results and retrieval of related items.
Who ever said that institutions were loathe to change? Well call him up and let him know, the Library of Congress, with their Prints and Photographs API has finally taken the REST API plunge. If this government institution can do it, maybe you can convince the head of your IT department that APIs are a good idea too.