Many museums have open catalogs so you can search their collections.

Things to be aware of:

• check out if you can physically go to the library and look at the material.
  
• if you can't go-USE INTERLIBRARY LOAN
  

The Museum of Modern Art

• DADABASE

The Metropolitan Museum of Arts Libraries

• WATSONLINE
• Information on educational resources at the Met libraries

New York Art Resources Consortium

• nyarc
  

The American Folk Art Museum

• Catalog: scroll down to click on link to catalog.

The Worcester Art Museum

• Bridges to Art

The Smithsonian Institutions Collections

• Search all catalogs or just the American Art Museum Collection

The British Museum

• Currently includes 279,713 objects in the online collection, of which 126,401 have one or more images.

The European Library

• Catalog listings and digitized items from the national libraries of Europe.

Getty Research Institute

• Library Catalog

• Contains over 500,000 bibliographic records for the 800,000 volumes of books, serials, and auction catalogs in the general and special collections, as well as descriptive records of approximately 3,000 archival and photograph collections.

Art Libraries

• Provides access to more than 6,000,000 primarily European bibliographic records, including articles in periodicals, conference papers, festschriften, exhibition catalogues, exhibition books, etc.

New York Public Library

• Access to more than 6.8 million records acquired from around the world in a variety of formats.