You can use any of these pictures for projects and don't have to worry about copyright.
Copyright Friendly Wiki
Links to lots of websites where you can find copyright friendly images (remember to cite your source).
NYPL Digital Gallery
Provides access to over 550,000 images digitized from primary sources and printed rarities in the collections of The New York Public Library, including vintage posters, historical maps, rare prints, and photographs. Great for history pics!
NC Wise Owl: Elementary Zone
This is an excellent resource for elementary reference material. We pay for the database, so you can use images from it for your projects. It includes links to the following sites: