I have seen this before in a template, but I have no idea how to do this

What I want to do is place a link (for arguments sake) at the bottom of the bottom

See link bella.marksdocs.com

As you can tell, I cant select the image, because it all the one image and I only want to link one part of it.

When I saw this before, it was like a floating clear box and you could stretch it out to cover as much of the graphic as you wish.

Does anyone know how to do this.

Cheeers