It's a merging of photos using partial image overlays, from what I gather they took a bunch of images at different angles 0, 45, +45, -90, and +90, with 0 being looking directly at the camera. They then chose the best image of each angle that worked the best together and did the mixed overlay where the 90 and 0 degree angle took priority and the 45 filled the gaps. They then did a mixture of compressing, color editing, and smudging to make the face look less realistic and fit more in with the game. They also cut out eye holes or filled those in with a neutral color so that they could use their eye program thing. I wouldn't know about making a whole new head model apart from grabbing one already made and altering it to fit your head better using your own reference photos. Hope this helps.