Thank you. I do the fur one stoke at a time using dodge, burn, and a skin tone brush at a single pixel size. I really enjoy doing these and love the way they turn out. It only takes a couple of hours to do.
I use it at about 30-50% opacity/strength with a 1 pixel brush. It helps add shadow hairs and highlighted hairs. It can also be used to shade and darken an area to make it look like a realistic shadow or point of light.
I use a high resolution photograph and use the dodge, burn, and smudge tools on a single pixel setting (In Photoshop or Paint Shop Pro). And then I just paint the fur on according to the way the lighting falls on the subject.