Image manipulation is a way of editing an image to highlight the main theme different than usual or something that is completely impossible naturally or something that means more than belief are the elements of image manipulation. special effects with correction are highly required for this kind of editing.
You should have seen horror movie banner or cover pages that something terrible is seen. Fantasy picture has the theme beyond natural objects or elements. thriller images have broken skin so natural but not real. All of them are actually done by image manipulation service.