If you are looking for images that document the history of our country try using the American Memory site at the Library of Congress. Many Americans aren't exactly sure what the Library of Congress is or what it does. LOC is the research library for Congress and the oldest federal cultural institution in the United States. It is the largest library in the world by shelf space and number of books. The head of the Library is the Librarian of Congress, currently James H. Billington.
Not only does the LOC have a huge digitized collection but they also have many digital and sound collections that are free to use. One of the many collections is the American Memory collection. This collection provides free access to written and spoken words, sound recordings, still and moving images, prints, maps, and sheet music that document the American experience. It is a digital record of American history and creativity.
The collection is divided into subject areas such as advertising, African American history, culture and folklife, performing arts and music and women’s history, but there are many more categories available for searching. The collection provides access to digital images of the sheet music and the sheet music covers. Here is some sheet music from their Civil War collection.
Make use of the collections at The Library Of Congress. They are free and for all of us to make use of.