Its a common enough question.

You can go through the laundry list.
Choice of model, adjusting morphs, skin textures, makeup, clothing, cloth textures, pose, lighting, composition, background and prop choice, render settings, postwork.  

I sometimes pointed out that a photographer actually makes less choices than a poser srtist does, because he may go out to a garden , and simply pick a view that looks nice. A poser person has to make the garden.

Theres a lot of debate if CGI is an art or a craft.