Social Media Buttons On Images

I saw a great implementation of social media buttons on images at this site: ... If you look at the image of lips, you will see in the lower right hand corner of the image that there are social media icons for facebook, twitter and pinterest. When you hover over the image, those boxes go from gray to being colored.

I would love to add this feature to the images in my posts on my website ... how can I do this?

Thanks for your help!

P.S. In case it is helpful, I have granted support access via the wpmu wordpress plugin...