Each of these sources for images offers you options for locating images that are available for use in academic work. Consult the rights information for individual images to be certain that they may be used. These resources are recommended because they provide ways for you to limit your searches to images that you may reuse.
Many University Libraries have "digital collections" or "digital archives." Frequently these images are in the public domain or the archive has permission to grant publication rights. Many of these libraries submit materials to Flickr Commons and Digital Public Library of America but many do not. Thee content in digital archives is often hidden from Google searches.
Look for digital collections at large universities in the state where your art object is or was located and search for images within that collection.