In this tutorial You will get basic idea about relighting 2d image characters. We are using Photoshop CS3 and adjustment layers masking techniques. Let's begin.
Add Your desire 2d cut out people inside composition.
Add two adjustment layers Brightness/Contrast in top of You character layer. Name them Shadow and Light.
Hold ALT key and click on lower area of adjustment layer tab. That way We made adjustment layers directly corespondent to character layer.
Double click on adjustment layer icon and adjust settings for Shadow and Light layers.
Invert mask by selecting each adjustment layer mask and press CTRL + i.
Select Light layer and chose your soft brush. Draw areas shat should be brighter from light.
Use this same method to mark shadow spots.
This tutorial is from http://www.viz-people.com. If you want to see more tutorials by visiting and registering in their site. You can also download freebies like cutout people, hdri, and models.