The neuropsychological phenomenon by which the brain interprets vague images as specific ones is called Pareidolia. A good example of this is when you see faces or animals in clouds. You can pretty much "see" familiar objects in almost anything.
The tendency for us to see faces in other objects has its origin in our neural architecture. It could be said that though many of us use our eyes to view the world, we really see by using our brain.
Here are a collection of happy faces. Do you see them all? Do you "feel" happy looking at them?