You may also want to visit the more expansive guide, WWI Primary and Secondary Sources
he Royal Marines Band Passing the Cenotaph …, 19 July 1919, From "The First World War" database collections
Search Digital Newspapers to find newspaper stories, photographs, advertising contemporaneous with the war. Search dates that might be anniversaries for memorials and remembrances (e.g., 10 years, 20 years, 25 years, 50 years later)
statistics on war atrocities from the British Library's World War One collection
Connect to pamphlets via the Hathi Trust Digital Library
Connect to pamphlets via Print at Penn.
Images taken from Europeana 1914-1918 searching "letters"