I have not looked at the PHP code but a few things I can think of off the top of my head 1) The detector doesn't like faces that are slightly rotated, either i

I have not looked at the PHP code but a few things I can think of off the top of my head 1) The detector doesn't like faces that are slightly rotated, either in-plane or out of plane. 2) The detector is "racist" in the way that most of the training images used were Caucasian people and therefore it works best on Caucasian. 3) It fails badly on kids because they aren't present in training data. Try normalizing your data a bit for that and see how it works out. If you want a detector that works better , simply use the one in openCV since it does a more thorough detection. The performance optimizations I did also cuts down the accuracy of the algorithm ( assuming his port has those too ).