How do you suppose that an image is found and purchased by someone who doesn't appear to have searched for any key word? How can someone find a picture of yours and purchase it if they never searched for a key word to begin with? Many, many of my pictures have been downloaded with nothing in the search column. It simply says "n/a".
For example, here is a picture that was downloaded recently but had an "n/a" listed under.
So, how are people finding these images? Is there a way to capitalize on these mysterious "n/a" downloads?