Click here for password help for home use.

Discovery Streaming Image Library
Change the WITHIN selection to "Images" and search for images using keywords or try out the advanced search.

Click here for password help for home use.

Smithsonian Institution's Photostream  (Free)
The Smithsonian Libraries has provided a selection of photographic portraits from the Dibner Library of the History of Science and Technology. Use the links you will find on the right side of their pages to see thumbnails of the collections:

OpenPhoto  (Free)
Hundreds of stock photos licensed for free commercial and non-commercial use

100 Milestone Documents  (Free)
This website provides images of 100 milestone documents from US history, compiled by the National Archives and Records Administration, and drawn primarily from its nationwide holdings. The documents chronicle United States history from 1776 to 1965.  See photos of the Declaration of Independence (1776), the Constitution of the US (1787) and more.

Wikipedia: Public Domain Image Resources  (Free)
A list of links to sources for public domain images. 

The presence of a resource on this list does not guarantee that all of the images in it are in the public domain. You are still responsible for checking the copyright status of images from the website you are using.

Pic4Learning

Pics4Learning is a copyright-friendly image library for teachers and students. The Pics4Learning collection consists of thousands of images that have been donated by students, teachers, and amateur photographers. Unlike many Internet sites, permission has been granted for teachers and students to use all of the images donated to the Pics4Learning collection.