I asked koz to do a tute on those hairtex w/hilites, but he said it's very complicated.  leaving them out makes it easier, unless yer taking photos of somebody's hair with a flash camera or in the sun, in which case it'll have hilites.  in case nobody mentioned this, try getting an orthographic photo, e.g. by scanning hair.  it may work pretty good for long straight hair, but maybe not too good for others.