How secure is Windows 8 photo gesture login?

How will Microsoft differentiate Windows 8 in an already crowded Windows OS user space? How about, for one, with the use of a photographic gesture security system for logging in? The idea of using a photo to identify and authenticate the user is not without some pretty obvious problems (ambient lighting, bad hair day, forgetting to shave could all screw up your chances of using the computer that day) which is why Microsoft developers have thought outside of the box on this one.