When you are dealing with flat surface this can be far easier than when adding shadows or reflation's to uneven terrain in post production. This is where displacement maps can be your friend.

Have you ever wanted to blend the text in Photoshop over an uneven surface area and make it look believable?
Have you ever wanted to blend logo design in Photoshop over an uneven surface area and make it look believable?
How about a tattoo mock up or create photo realistic shadows as if they were always part of the picture?
And how about GOBO effect to your photos? Shadows from a window frame etc.
You will sooner or later have to incorporate the help of displacement maps. What are they and how to use them, was the topic of the last series of tutorials and you can find it here on Skillshare.
This course is called "Introduction To Compositing In Photoshop; Bringing Shadow to the light" and as the title suggests it builds upon the previous course. We will be using same basic techniques to add shadows to the model and I will also teach you about the importance of shadows and we will explore various ways in which you can use the techniques I'm teaching in wide variety of cases.
I will also talk about Depth Masks. A way to simulate shallow depth of field, and how it can be used solo or in combination with the Displacement Maps to create, realistic looking, complex composites in Photoshop.
Content Source:

https://www.skillshare.com/classes/Introduction-To-Compositing-In-Photoshop-Bringing-Shadow-to-the-light/1788549428