What makes an image haunting or disturbing?

There are several visual cues in here that put us at unease. The clown.. his mouth.. the arm on the left. The sheer size of the clown. The old black and white picture and the slight scratches on it make it look 'real' even though im sure its staged and fake. There are kids nearby and the dad has blood on his face. One can find peace in the mother's eyes, though, but only for a moment.