You seem to be new to the topic since you are confusing face detection and face recognition. Face detection is a relatively simple affair, given an image determ

You seem to be new to the topic since you are confusing face detection and face recognition. Face detection is a relatively simple affair, given an image determine a bounding box for each candidate face. OpenCV (http://opencv.willowgarage.com/wiki/ http://opencv.willowgarage.com/wiki/) is an excellent library with a lot of computer vision related functions. Out of the box it has an example program for face detection which performs quite well with the default Haar model files it comes with. Detection rates of higher than 95% are not uncommon for photos with clean faces. So, you can set up a fairly good face detector in a day or so. Face recognition, on the other hand, is a totally different beast. The bounding boxes you detect in the detection step are fed into classifiers that you should train. If you are new to this field I don't recommend you do this training or develop your own algorithms, since it's a complicated problem. You say most photo software does this, but generally these are offerings from large companies, e.g. Picasa, that have years of face recognition expertise behind that product. My recommendation is (i) to abandon the recognition idea (gulp! this may be hard to stomach but the energy may be better spent somewhere else, as this is very hard to get right) or (ii) if you insist, use an online API (e.g. http://developers.face.com/docs/ http://developers.face.com/docs/).