If you ask yourself this question, this will be handy for you.
Although very detailed 3d models of human beings are starting to emerge recently, the most common resource is to use real photographs of people.
This new option to use 3d models has an obvious advantage: it does not need any post production work. The 3d model is perfectly integrated in the scene to be illuminated like the other elements that compose it.
The supply of these types of models is growing more and more, but is currently limited. No viewer likes to meet the people he uses in composing his images in the works of others.
For these reasons, it is usual to visit the composition cut out people websites.
I leave you a selection of the sites that I consider most interesting.
I always recommend that you do not focus solely on free resources but, in this case, talking about cutout people, you will find extensive collections and many of them free.