Well okay here is what I do!  I take and Image from the front and from the side and a close up of the eyes I have a Canon Rebel XTI and It Works great!! Be sure not to shoot it with a on camera flash. the washes out the skin tones.. the best posible scenereo is to use studio lighting.. if the is not available,  use outdoor lighting I found that a overcast day or partly cloudy day works best so again you dont get that overexposed texture... Okay sorry I tend to ramble on..
Okay then I take one of the existing textures and use it as a template from face for V4.  I like to use Marja or Erica they work great . I open it up in Photoshop. I Take my face Image from front and the sides and start to spread out the image over top of the other texture. this takes a bit to get the hang of it but once you have learned it,  there is no turning back..IT IS THE BEST WAY!!! trust me I have done it a few times..Also rember to make your bump maps.. This is to achieve the best and realistic results.. I am a photoshop Artist by trade and found to be the most accurate way  at least it has worked for me..