How do I find a distance between the contour pixels of an irregular image and the center of mass of that image?

edit

I have a binarized image by Otsu Threshold. I'm new in C++ and Opencv. I try this, but don't work.

      #include <iostream>
    #include "opencv2/imgproc/imgproc.hpp"
   #include "opencv2/highgui/highgui.hpp"
   #include <stdlib.h>
   #include <stdio.h>

using namespace cv;
using namespace std;

int main(int argc, char** argv)
{
    cv::Mat img = cv::imread("melanoma_abertura_cortada_NAOINVERT.png");

    if (img.empty())
    {
        std::cout << "!!! imread() failed to open target image" << std::endl;
        return -1;
    }
    cv::Mat img_canny;

    vector<vector<Point> > contours;
    vector<Vec4i> hierarchy;

    Canny(img, img_canny, 80, 20);


    findContours(img_canny, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_NONE, Point(0, 0));

// Get the moments
    vector<Moments> mu(contours.size());
    for (int i = 0; i < contours.size(); i++)
    {
        mu[i] = moments(contours[i], false);
    }

    ///  Get the mass centers:
    vector<Point2f> mc(contours.size());
    for (int i = 0; i < contours.size(); i++)
    {
        mc[i] = Point2d(mu[i].m10 / mu[i].m00, mu[i].m01 / mu[i].m00);


    }

    for (size_t cC = 0; cC < contours.size(); ++cC)  
        for (size_t cP = 0; cP < contours[cC].size(); cP++)
        {
            Point currentContourPixel = contours[cC][cP];
        }

        Mat  magnitudee;

        magnitude(mc, contours.size(), magnitudee);

    cv::waitKey(0);
    return 0;
}