Image manipulation is the art of combining and altering photographs in a plausible manner.
The above samples are some more extreme examples of compositing, however most images you see in print have been manipulated in some unnoticable manner like whitening teeth or removing blemishes to make the image more pleasing or compositing images like moving people onto a different background or removing a background completely and floating a product on a white background. On the Graphic Design page you will find more examples of this milder form of manipulation.