The one with expected behavior.

gistfile1.cpp

#define _CRTDBG_MAP_ALLOC
#include <crtdbg.h>

#include <opencv2/opencv.hpp>
#include "opencv2/core/core.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/calib3d/calib3d.hpp"
#include "opencv2/highgui/highgui.hpp"


int main(void)
{
	_CrtSetDbgFlag(_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG) | _CRTDBG_LEAK_CHECK_DF);
	{
		cv::Mat xx = cv::imread("B:/cc.png");
		cv::imshow("win title", xx);
	}
	//int *p = new int;

	return 0;
}

No output because there's no memory leak.

But _CrtSetDbgFlag() have actually enabled the memory leak detection.
_CrtDumpMemoryLeaks() is called automatically and implicitly at the termination of this program because we have used _CrtSetDbgFlag properly.

Try uncomment //int *p = new int;