However, much more reliable solutions exist now. We’re going to use a method invented in 2005 called Histogram of Oriented Gradients — or just HOG for short.
Machine Learning is Fun! Part 4: Modern Face Recognition with Deep Learning
Adam Geitgey
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This HOG method is outdated. Now neural networks are used for face detection too. See for example CVPR2015 ‘A Convolutional Neural Network Cascade for Face Detection’ and many other papers