[iOS] Face detection

http://developer.apple.com/library/ios/#documentation/CoreImage/Reference/CIFaceFeature/Reference/Reference.html
http://developer.apple.com/library/ios/#documentation/GraphicsImaging/Reference/CoreImagingRef/_index.html
http://developer.apple.com/library/ios/#documentation/CoreImage/Reference/CIDetector_Ref/Reference/Reference.html#//apple_ref/doc/uid/TP40010974
http://developer.apple.com/library/ios/#samplecode/SquareCam/Introduction/Intro.html