How find matching percentage of two images

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

using namespace std;
using namespace cv;

/// Global Variables
Mat img; Mat templ; Mat result;
char* image_window = "Source Image";
char* result_window = "Result window";

int match_method;
int max_Trackbar = 5;

/// Function Headers
void MatchingMethod(int, void*);

/** @function main */
int main(int argc, char** argv)
{
	/// Load image and template
	img = imread("IMG_20160214_092738.jpg", 1);
	cv::resize(img, img, cv::Size(), 0.35, 0.3);
	templ = imread("IMG_20160131_120252.jpg", 1);
	cv::resize(templ, templ, cv::Size(), 0.25, 0.25);
	/// Create windows
	namedWindow(image_window, CV_WINDOW_AUTOSIZE);
	namedWindow(result_window, CV_WINDOW_AUTOSIZE);

	/// Create Trackbar
	char* trackbar_label = "Method: \n 0: SQDIFF \n 1: SQDIFF NORMED \n 2: TM CCORR \n 3: TM CCORR NORMED \n 4: TM COEFF \n 5: TM COEFF NORMED";
	createTrackbar(trackbar_label, image_window, &match_method, max_Trackbar, MatchingMethod);
	//match_method
	MatchingMethod(0, 0);

	waitKey(0);
	return 0;
}

/**
* @function MatchingMethod
* @brief Trackbar callback
*/
void MatchingMethod(int, void*)
{
	/// Source image to display
	Mat img_display;
	img.copyTo(img_display);

	/// Create the result matrix
	int result_cols = img.cols - templ.cols + 1;
	int result_rows = img.rows - templ.rows + 1;

	result.create(result_rows, result_cols, CV_32FC1);

	/// Do the Matching and Normalize
	matchTemplate(img, templ, result, match_method);
	normalize(result, result, 0, 1, NORM_MINMAX, -1, Mat());

	/// Localizing the best match with minMaxLoc
	double minVal; double maxVal; Point minLoc; Point maxLoc;
	Point matchLoc;
	
	minMaxLoc(result, &minVal, &maxVal, &minLoc, &maxLoc, Mat());
	cout << minVal << "***" << maxVal << endl;
	/// For SQDIFF and SQDIFF_NORMED, the best matches are lower values. For all the other methods, the higher the better
	if (match_method == CV_TM_SQDIFF || match_method == CV_TM_SQDIFF_NORMED)
	{
		matchLoc = minLoc;
	}
	else
	{
		matchLoc = maxLoc;
	}

	/// Show me what you got
	rectangle(img_display, matchLoc, Point(matchLoc.x + templ.cols, matchLoc.y + templ.rows), Scalar::all(0), 2, 8, 0);
	rectangle(result, matchLoc, Point(matchLoc.x + templ.cols, matchLoc.y + templ.rows), Scalar::all(0), 2, 8, 0);

	imshow(image_window, img_display);
	imshow(result_window, result);

	return;
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