These are the slides to my talk for XCake on using OpenCV for face recognition on iOS. It should be noted that the first half of the talk deals with using OpenCV to also detect faces and so applies to any platform you can use OpenCV on. The simplified code sample on slide 14 should more or less work for you on non-iOS implementations.
Links
Slide 4: https://en.wikipedia.org/wiki/Prosopagnosia
Slide 6: http://opencv.org/
Slide 9: http://coding-robin.de/2013/07/22/train-your-own-opencv-haar-classifier.html
Slide 10: http://docs.opencv.org/modules/contrib/doc/facerec/facerec_tutorial.html
Slide 25: http://www.rekognition.com/
https://www.bioid.com/solutions/solutions-by-application/bioid-for-facedotcom.html
http://api.animetrics.com
http://www.identitykit.it/
http://www.skybiometry.com/
Slide 27: https://github.com/kmonaghan/FaceRecognition
Other
520 – What’s New in Camera Capture from WWDC 2012 talks about CIDetector and AVCaptureMetadataOutput from about the 19 minute mark. You should look at the sample code from that talk (StacheCam) for details on how to implement CIDetector and AVCaptureMedataOutput rather than the SquareCam project referenced in the Apple Documentation.