I would suggest you make a black and white copy of a photo so you can see the gray scale of a particular photo. You may want to just copy a face and enlarge it to a size thats workable. Use that as a guide for adding fabrics in different values in the areas that show from dark to light.
It's amazing once you use black and white it so much easier to get the shadows and shapes easier.
Use FM thread painting techinques for very fine lines using a dissappearing marker to help you stitch where you intend.
Many makers use raw edge fusible applique. making two copies one the use as the cutting guide/pattern the other as the final placement guide . Do note that cutting all at once typically will leave you confused as to what goes where . go slowly cutting /working on sections at a time.