Years ago I bought an interesting image at a photo show. It was completely unidentified--no name and no photographer's markings.
This was a great test for Google Images. To see if there are matches to a particular image you can either cut and paste a URL in the search box or upload an image to the search box. I choose the latter.
In this case, there was an exact match on the iCollector.com website.
Google Images isn't 100% effective. It provides you with exact matches and then visually similar pictures. For the purpose of this search, Google found other carte des visite images of people posed like von Moltke and some that don't have much in common with the image I searched.
Identity confirmed. Case closed. Thank you to Paul Silverstone for positively identifying an image from my collection.