Image Movement on Cursor Movement

I am having the hardest time trying to figure out what I need to look up to find a solution. I swear I've seen it before, but for the life of me can't figure out where to look.

Basically, I want an image as a background, and when the cursor moves around the image, it (the image) moves slightly and warps. Like a parallax effect almost? Any help or pointers is much appreciated, thanks.