When you click an image in Google Image search, the new screen shows the image at the top with an option to "show bigger image", then below it shows the webpage in a frame. It fetched the webpage and shows it in a frame. BUT YOU ARE STILL ON GOOGLE'S WEBSITE. So doesn't this mean that your logs don't show real visitors, but only fetches from Google. In other words, nobody actually comes to your own site.
But I believe that they can still do everything on your site but yes it is still through Google's iFrame.