In case you didn’t see this over at Pandia — Pandia has noted an interesting feature Google image search. If you search for something and then add &imgtype=face to the result URL, you will get only results that have faces in them.
Pandia mentioned doing this in conjunction with a name search, but I found getting the results was much more dramatic when I did the search in conjunction with a fairly pedestrian search like lightning. That search by itself gets almost two million results. That search with the &imgtype=face result URL modifier narrows it down to just under 25,000, with images including dogs, reggae bands, Native Americans, and the comic book superhero Black Lightning.
Now if this only worked with Google Product Search….