Yes, including at least one picture is best. And yes, I have the same problem sometimes. What works for me is to do a little free-association. If there is no perfect picture, ask yourself: What picture does your hub remind you of? Then go to Wikipedia.
I wrote a hub about a strength-training exercise of my own invention for the upper legs. I knew that I'd never find the right picture on the Internet. And I'm not particularly photogenic; so I didn't want to ask a friend to immortalize me, while demonstrating this particular exercise.
My solution: A photo of a Gorilla from the Wikipedia article. Everyone enjoys pictures of animals. :-)