We all time to time get visitors from Google Images and usually they just see our site in a frame, just copy the needed image and then forget about that site. Never wanted to have them REALLY land on your site? So they maybe finding something interesting there and becoming one of your repeated visitors?
If so, there is a solution and it is dumb simple:

Create refresh.js with the following code:
if (window != top) top.location = self.location

and put it say in the JS folder of your site. Then in the HEAD of your site place
<script language="javascript" src="http://www.yoursite.com/js/refresh.js"></script>
with the correct location to refresh.js.

Don't ask me if it in anyway break Google Policies or anything like that. I have NO IDEA about that, but i don't think it should. Plus, you can encode the JS anytime