The British Museum offers free use of images in their collection under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) license. If you do a search with the term ‘revolution’ you will receive coins, prints, portraits and a wide range of objects associated with the various revolutions in history, approximately 4,000 results. You need to register with them first, and if you want to have higher resolution images, they will send them to your email account, see https://www.britishmuseum.org/collection
GALLICA is the French National Biblotheque which has free access to a large image database on images. One of the collections is entitled Revolution (1789-1799). http://gallica.bnf.fr/html/und/images/la-revolution-1789-1799
French Revolution Digital Archive Standford University, for the image collection see https://frda.stanford.edu/ /en/images. Free for use if not commercial. Copyright statement: Use and reproduction: This image(s) is a digital reproduction of works from the collections of the Bibliothèque nationale de France that are no longer protected by intellectual property rights. The use of these contents for commercial purposes is subject to payment and covered by a license. Commercial use includes the resale of the contents in the form of prepared products or the supply of services. For commercial use, contact: firstname.lastname@example.org. The use of these contents for non-commercial purposes is free of charge, subject to compliance with applicable French legislation and notably the inclusion of the source’s statement.
American Revolution http://www.digitalhistory.uh.edu/references/images.cfm Lists several different sites pertaining to the Civil War, Slavery, and other related aspects.
Russian Revolution Getty Institute.
New York Public Library Digital Collection http://digitalcollections.nypl.org/
Smithsonian Institute Digital Collection
John Hopkins – Large Site for Latin American Digital Collections, e.g. Mexican Revolution