Hi Kevin,
If the photo is private it won't appear as a thumbnail on surname index pages or elsewhere.
Photo privacy isn't set directly. It depends on the privacy levels of the people in the photo. If anyone tagged in the photo is public, the photo is public.
http://www.wikitree.com/wiki/Photo_Privacy
So, in your case, you'd need to either remove public people from the photo or make the people private.
Chris
