If you are seeking a photograph of the Armed Guard crew aboard WILLIAM CLARK, it is unlikely that you will be able to find same. Although it was apparently typical that an Armed Guard crew would have a group photograph at some point, probably before embarking on a ship, there is no centralized online depository of such photographs. It is possible that the National Archives may have original photographs in its collection. You may wish to research the World War II photographic collection at the Archives beginning with https://www.archives.gov/research/military/ww2/photos.
If you are interested in a photograph of the ship itself, I have found two instances, both of relatively poor quality and both actually the same photograph, at https://uboat.net/allies/merchants/ship/2374.html and at https://www.armed-guard.com/wmclark.jpg. For sources of original photographs or copies of original photographs of World War II-era merchant vessels, see http://usmm.org/photosource.html.
Ron Carlson, Webmaster
Armed Guard / Merchant Marine website