Sound and images (both still pictures and video) can help describe and understand the past. If from the period being studied, they can also be used as primary sources. One of the largest collection of this kind is American Memory, a digital library created by the Library of Congress to contain primary source and archival material relating to American culture and history: print, manuscripts, photographs, moving pictures and recorded sound. It has more than 150 collections and continues to grow.
But there are many other collections, large and small. To explore them, move your mouse to the tab at the top of this page for "Audio, Images, Video" and choose one of the sub-pages.