I recently finished this personal piece and thought I would share some samples
from my collage process:
I start with a simple hand drawn sketch that I scan it into Photoshop.
On top of the sketch I build each character with layers of flat color and begin to
lay in my larger background shadows.
After I've created all of the large shapes, I place papers/textures within the
shapes by using clipping masks. All facial details are added and to complete
the illustration I lay in shadows to give the figures a raised effect.