To locate primary sources, you can check our library catalog or the web using your (key words) PLUS any combination of these terms: primary sources, digital library, oral history, repository, photographs, archive, FINDING AID, declassified documents. The best sources are government (national, state or regional sources) or college and university collections. Government agencies have digital collections, too, such as the US Naval Academy. Here is a WWI image collection about US propganda in Japan.
Also check: Library of Congress, US National Archives, US State Archives, and National Archives (UK), State Historical Societies and Journals. College & University Digital Collections (with search term digital collection or digital library) add new collections all of the time.
See more database options from SHU here:University Library Resources