FisherFace detect me even if my image is note in database

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System information (version) - OpenCV => 2.4.9.1 - Operating System / Platform => Linux Ubuntu 64 Bit - Compiler => CMake 3.5.1

Detailed description

I use imgshow to prompt the webcam capture and add a rectangle and the subject found with FisherFace algorithm AT&T orl_face photo base. The problem is FisherFace algorithm detect me even if I am not in the database, it confuses me with 2 subjects... I changed the minNeighbours parameter but it doesn't change anything.

Thanks to the FaceRecognizer() Thresholds documentation, I updated the code :

// Create a FaceRecognizer and train it on the given images:
Ptr<FaceRecognizer> model = createFisherFaceRecognizer(10,0.0);
model->train(images, labels);
// The following line reads the threshold from the Eigenfaces model:
double current_threshold = model->getDouble("threshold");
// And this line sets the threshold to 0.0:
model->set("threshold", 0.0);
.
.
.
haar_cascade.detectMultiScale(gray, faces, 1.1, 5,0, cvSize(30,30), cvSize(30,30));
.
.
.
Mat face_resized;
cv::resize(face, face_resized, Size(im_width, im_height), 1.0, 1.0, INTER_CUBIC);
// Now perform the prediction, see how easy that is:
int prediction = model->predict(face_resized);
// And finally write all we've found out to the original image!
// First of all draw a green rectangle around the detected face:
cout << prediction << endl;

(See full code just below)

Steps to reproduce

#include "opencv2/core/core.hpp"
#include "opencv2/contrib/contrib.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/objdetect/objdetect.hpp"

#include <iostream>
#include <fstream>
#include <sstream>

using namespace cv;
using namespace std;

static void read_csv(const string& filename, vector<Mat>& images, vector<int>& labels, char separator = ';') {
    std::ifstream file(filename.c_str(), ifstream::in);
    if (!file) {

        string error_message = "No valid input file was given, please check the given filename.";
        CV_Error(CV_StsBadArg, error_message);
    }
    string line, path, classlabel;
    while (getline(file, line)) {
        stringstream liness(line);
        getline(liness, path, separator);
        getline(liness, classlabel);
        if(!path.empty() && !classlabel.empty()) {
            Mat m = imread(path, 1);
            if (m.empty())
            {
                cerr << path << " could not be read." << endl;
                continue;
            }
            Mat m2;
            cvtColor(m,m2,CV_BGR2GRAY);
            images.push_back(m2);
            labels.push_back(atoi(classlabel.c_str()));
        }
    }
    cout << endl << "Read finish";
}

int main(int argc, const char *argv[]) {
    if (argc != 4) {
        cout << "usage: " << argv[0] << " </path/to/haar_cascade> </path/to/csv.ext> </path/to/device id>" << endl;
        cout << "\t </path/to/haar_cascade> -- Path to the Haar Cascade for face detection." << endl;
        cout << "\t </path/to/csv.ext> -- Path to the CSV file with the face database." << endl;
        cout << "\t <device id> -- The webcam device id to grab frames from." << endl;
        exit(1);
    }
    string fn_haar = string(argv[1]);
    string fn_csv = string(argv[2]);
    int deviceId = atoi(argv[3]);
    vector<Mat> images;
    vector<int> labels;
    try {
        read_csv(fn_csv, images, labels);
    } catch (cv::Exception& e) {
        cerr << "Error opening file \"" << fn_csv << "\". Reason: " << e.msg << endl;
        // nothing more we can do
        exit(1);
    }
    int im_width = images[0].cols;
    int im_height = images[0].rows;
    Ptr<FaceRecognizer> model = createFisherFaceRecognizer(10,0.0);
    model->train(images, labels);
    double current_threshold = model->getDouble("threshold");
    model->set("threshold", 0.0);
    CascadeClassifier haar_cascade;
    haar_cascade.load(fn_haar ...