The Library of Congress is a treasure trove of historical information. The huge collection of Prints and Photographs is housed here, and you will see links to many other digital collections that are available online.
You can use Google to search for images.
Once you get search results, use the options on the left of your screen to limit to images by:
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The Instructional Image Catalog is a digital library of art images licensed to University Libraries. Use the Instructional Image Catalog to locate art images for instruction and research. Search for images by creator, title, keyword, date, medium, culture, stylistic period, subject, and more. Search results display a thumbnail image and brief descriptive text. To learn more about an image, double-click the thumbnail; a larger image is then displayed with the catalog record appearing on the left. Instructional Image Catalog uses the LUNA Insight image database system and incorporates image group saving, presentation, and export features. All images are copyrighted and licensed to University Libraries for classroom, private study, and research use by members of the WMU community. BroncoNetID required for login.
Contains over one million art images in the arts, architecture, humanities, and social sciences, intended for non-profit, scholarly or educational use. Institutions, organizations, and individuals from around the world have contributed collections to this searchable digital library. Tools are also provided to create presentations using Artstor images combined with images from users personal collections.