Help me with facial recognition

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Hello! I'm starting with opencv and python. I would like to make a program that makes facial recognition. Read enough about opencv and python. I did some tests with the correlation matrix. I also did tests with samples available and read the tutorial "Philipp Wagner". However, the problem is that I am unable to understand how an informed picture for me may be recognized. Nor do I understand the difference between "eigenfaces" and "fisherfaces". Could anyone help me? (Sorry for my poor english)