Photoshop provides a pretty easy way to make some fairly realistic looking facial hair. This tutorial will show you how fun and easy it is to add facial hair to a photo.
Select the Brush tool B and under the Brush menu find the Dune Brush and select it.
TIP: You can choose to view your brushes by selecting "Text Only" from your brush menu.
Use the Eyedropper tool I and sample the color of your person's hair. Hold the Alt and sample another, slightly different, color of your person's hair.
Now we're going to go through the wonderful Brushes Palette. You can open it by going to Window > Brushes or by pressing F5.
This is where all the magic happens. Under "Shape Dynamics" we're going to: increase the Angle Jitter a bit, decrease the Roundness Jitter a bit, and check both the Flip X Jitter and Flip Y Jitter checkboxes.
Under "Scattering" we can control how dense we want the hair to be. We're going to start her off with a little 5'o click shadow. So I'll set the Scatter to around 200% and the Count to 2.
Under "Color Dynamics" I'm just going to increase the Hue Jitter slightly.
Now I'll just create a new layer Ctrl + Shift + N and decrease my brush size to something small... like 5 or 6. Then just start painting in the appropriate areas.
Now let's say we wanted to make the hair a little thicker. All we have to do is increase the Brush size slightly (8 or 9 here) and start painting again.
Just keep playing with the "Scattering" settings, Brush size, and color to get different types of hair. You can even play around with the Layer modes and duplicating the layers.
See? So much fun.
Since a few people were having troubles with the brushes, you can download my brushes here. You might see a few extra brushes, but the hair one is at the bottom.