Looks like I'm a bit late to the discussion. (I only just recently discovered Vertigo due to the shakeup in this year's Sight & Sound poll.)
I too was curious about the face. There are various mentions here and there on the web that this shot features Kim Novak's face, but it certainly doesn't look like Kim Novak (just look at the eyebrows).
When I saw this thread, I was inspired to construct a composite from multiple screenshots throughout the pan, to help get a better idea of the face as a whole; it's not perfect, as there was some zoom and a tiny bit of angle change/parallax d