There are many great research sources on the web for images.
A few to try:
Atla Digital Library -- historical and archival content in religion and theology -- Search "Hartford Seminary" to access images from our own library collections.
Digital Public Library of America – DPLA
Theological Commons Photographic Files
Getty Images Archival Photos – this site sells photos to download, but you may view them or download temporary complimentary copies
Google Images can be helpful if your search is very specific.