How does a clothing company use one model photo for endless clothing options?

When you look at Under Armour’s site (or most other clothing sites), it looks like they have one photo of a model, then they put dozens of different clothing items on him. Clearly it is the same face (expression) and head, the body is always in the same position/shape. They couldn’t be reposing this guy over and over. Is that all Photoshop? Or is there some kind of special software that the clothing industry uses? Are they using a mannequin, or something? They do a great job of making the photos look like the model is actually wearing the outfit. You are hard pressed to find signs of retouching.