The Library of Congress hosts an online collection of more than 500 political cartoons and caricatures from U.S. History. You can search the collection by keyword and image type. Along with the images you will find links to related resources from the Library of Congress. You could use these public domain works to help students understand the political perspectives surrounding significant political events in U.S. History. A good model for political cartoon-based lesson plans can be found on Cartoons for the Classroom.