Doing facial recognition well, recognizing with different angles, and different facial hair, different hats, and so on, is not easy. It would take you a fair bit of research and experimentation to be close to Google's or Apple's success. A couple of years ago, Microsoft launched its facial recognition technology to much publicity, the greater part of which was due to the many failures.
Myself, I would probably purchase a product rather than try to write it myself. Or I would look for freeware. facedetection.com has a useful-looking list of available products.
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