As a producer it's my role to be involved in planning as well as supervising the photoshoots. I'll find appropriate photographers, models and goods for the gig and make sure that the end product meets the agreed quality standards.
Photomontage is the process of making a composite photograph by cutting and joining various photographs into a seamless photographic print. This method usually includes painting on top of the images and possibly 3D elements.
Retouching is an image editing technique that photographers use to enhance and correct the photograph after the original shooting has taken place.