Image Collection-based Internet Search Engines
Sometimes, when you have a very specific image need, you're better off going to a digital library or a community-based photo collection like Flickr. These resources are created by humans rather than web crawlers, and so often can allow for more focused searching.
Flickr
Images are often available at a higher quality, if the individual uploaded the image at the resolution taken by their camera. You can limit a search to only those images licensed under a creative commons license (http://www.flickr.com/creativecommons/). Then you know you are really permitted to use the photos you have found. Note though, that these images are taken by the general public, so the quality of photography varies widely. Images are almost exclusively photographs — you will find few drawings, maps, etc. here.
Library of Congress American Memory Project
The Library of Congress has digitized a wide range of material from its collections and made it freely available on the web. To search images, click More browse options, then choose Photos, prints at the right under "Browse Collections Containing". Note, however, that these are all older images, useful for studying the history of a site, and are generally not particularly high resolution.
SPIRO
This is the online image library of the University of California at Berkeley. Its primary focus is architecture, but you can use the search options to locate images of sites, objects, etc.
