Retouching is the process of getting an image ready for final presentation to a printer. This can involve a variety of techniques and processes, can be very subtle or dramatic but every image that you see used in advertising will be subjected to some form of enhancement even if it is only to remove dust, color correcting and sharpening.
Removing flaws such as blemishes or unwanted elements such as a tree growing over someone's head, graininess from low quality cameras are often addressed in retouching. Creative retouching is an art form for commercial use to create more sleek and interesting images for advertisements. Image compositing is a prominent discipline where the artist uses multiple photos, 3D graphics and extra elements, locations and backgrounds. This technique is widely used when conventional photography would be technically too difficult or impossible to shoot on location or in a studio.