#include "stdafx.h"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
using namespace cv;
using namespace std;
//using namespace cv::xfeatures2d;
//using namespace cv::ml;

Mat src;
bool down = false;
Point prept = Point(-1, -1);
Point curpt = Point(-1, -1);
void on_mouse(int event, int x, int y, int flags, void* ustc)
{

	if (event == CV_EVENT_LBUTTONDOWN)    //右键按下
	{
		prept = Point(x, y);
		cout << x << " " << y << endl;
		down = true;
	}
	else if (event == CV_EVENT_LBUTTONUP)     //右键放开
		down = false;

	if (down == true && event == CV_EVENT_MOUSEMOVE)    //右键按下且鼠标移动
	{
		curpt = cvPoint(x, y);
		line(src, prept, curpt, Scalar(255, 0, 0), 5);
		waitKey(5);        //可以解决画图时卡顿的问题
		imshow("src", src);
		prept = curpt;
	}
}

int main()
{
	src = imread("C:\\Users\\Administrator\\Desktop\\3.png", 1);

	cvNamedWindow("src");
	cvSetMouseCallback("src", on_mouse, 0);//关键内置函数

	imshow("src", src);
	cvWaitKey(0);
	cvDestroyAllWindows();
	return 0;
}

其中#include <opencv2/highgui/highgui_c.h>可以加入此头文件，防止后面的cvNameWindow等函数无法识别。此外#include "stdafx.h"可以删除。
CV_EVENT_LBUTTONDOWN可以将CV_去掉，如果出现无法识别。