Code snippets for my OpenCV face recognition tutorial, in which I show how to build an application which recognizes a specific person in a video. Full code at: https://bitbucket.org/EyalAr/person-recognizer

InitPersonRecognizer.cpp

#define PERSON_LABEL = 10 //some arbitrary label

//LBPH face recognizer parameters:
#define RADIUS    1
#define NEIGHBORS 8
#define GRID_X    8
#define GRID_Y    8
#define THRESHOLD 130.0

//create a LBPH face recognizer model:
Ptr<FaceRecognizer> model =
    createLBPHFaceRecognizer(RADIUS, NEIGHBORS, GRID_X, GRID_Y, THRESHOLD);
    
vector<Mat> imgs = /* Populate this vector with images of the
                      face of the person to be recognized */;
                       
//Initialize a vector of labels. All labels have the same value
//since all faces belong to the same person.
vector<int> labels(imgs.size());
for (vector<int>::iterator it = labels.begin();
     it != labels.end();
     *(it++) = PERSON_LABEL);
     
//Train the face recognizer to recognize the face of the perosn:
model->train(imgs, labels);

/* Now the model is ready to recognize faces. */

RecognizePerson.cpp

Mat face = /* The image of the face to be recognized */;
Mat gray;

//convert the face to grayscale:
cvtColor(face, gray, CV_BGR2GRAY);

int label = -1;
double confidence = 0;

//Make the prediction:
model->predict(gray, label, confidence);

if (label == PERSON_LABEL){
    /* Face recognized as our person. */
    cout << "Person recognized with confidence of " << confidence << endl;
}
else{
    cout << "Face not recognized." << endl;
}