HELP! Overlay For Google Image Search - How does this site do this?

With the new Google image search stealing traffic I'm trying to figure out a way to make visitors go to the site after searching for images. The only site I know that came up with a solution I think would work is fansshare. When you click on a image that's on their site it shows the picture then an overlay that says "Click Here For Full Resolution".

Here is the site on Google Images:

How the hell do they do that?

http://pixabay.com/en/blog/posts/hotlinking-protection-and-watermarking-for-google-32/

i don't know if google will penalize you though