学习了他人的用鼠标截图的功能，建立在opencv2的基础上去的

// 鼠标截取图像.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"

#include 
#include 
#include 

using namespace cv;

cv::Mat org,dst,img,tmp;
void on_mouse(int event,int x,int y,int flags,void *ustc)//event鼠标事件代号，x,y鼠标坐标，flags拖拽和键盘操作的代号
{
	static Point pre_pt = (-1,-1);//初始坐标
	static Point cur_pt = (-1,-1);//实时坐标
	char temp[16];
	if (event == CV_EVENT_LBUTTONDOWN)//左键按下，读取初始坐标，并在图像上该点处划圆
	{
		org.copyTo(img);//将原始图片复制到img中
		sprintf(temp,"(%d,%d)",x,y);
		pre_pt = Point(x,y);
		putText(img,temp,pre_pt,FONT_HERSHEY_SIMPLEX,0.5,Scalar(0,0,0,255),1,8);//在窗口上显示坐标
		circle(img,pre_pt,2,Scalar(255,0,0,0),CV_FILLED,CV_AA,0);//划圆
		imshow("img",img);
	}
	else if (event == CV_EVENT_MOUSEMOVE && !(flags & CV_EVENT_FLAG_LBUTTON))//左键没有按下的情况下鼠标移动的处理函数
	{
		img.copyTo(tmp);//将img复制到临时图像tmp上，用于显示实时坐标
		sprintf(temp,"(%d,%d)",x,y);
		cur_pt = Point(x,y);
		putText(tmp,temp,cur_pt,FONT_HERSHEY_SIMPLEX,0.5,Scalar(0,0,0,255));//只是实时显示鼠标移动的坐标
		imshow("img",tmp);
	}
	else if (event == CV_EVENT_MOUSEMOVE && (flags & CV_EVENT_FLAG_LBUTTON))//左键按下时，鼠标移动，则在图像上划矩形
	{
		img.copyTo(tmp);
		sprintf(temp,"(%d,%d)",x,y);
		cur_pt = Point(x,y);
		putText(tmp,temp,cur_pt,FONT_HERSHEY_SIMPLEX,0.5,Scalar(0,0,0,255));
		rectangle(tmp,pre_pt,cur_pt,Scalar(0,255,0,0),1,8,0);//在临时图像上实时显示鼠标拖动时形成的矩形
		imshow("img",tmp);
	}
	else if (event == CV_EVENT_LBUTTONUP)//左键松开，将在图像上划矩形
	{
		org.copyTo(img);
		sprintf(temp,"(%d,%d)",x,y);
		cur_pt = Point(x,y);
		putText(img,temp,cur_pt,FONT_HERSHEY_SIMPLEX,0.5,Scalar(0,0,0,255));
		circle(img,pre_pt,2,Scalar(255,0,0,0),CV_FILLED,CV_AA,0);
		rectangle(img,pre_pt,cur_pt,Scalar(0,255,0,0),1,8,0);//根据初始点和结束点，将矩形画到img上
		imshow("img",img);
		img.copyTo(tmp);
		//截取矩形包围的图像，并保存到dst中
		int width = abs(pre_pt.x - cur_pt.x);
		int height = abs(pre_pt.y - cur_pt.y);
		if (width == 0 || height == 0)
		{
			printf("width == 0 || height == 0");
			return;
		}
		dst = org(Rect(min(cur_pt.x,pre_pt.x),min(cur_pt.y,pre_pt.y),width,height));
		namedWindow("dst");
		imshow("dst",dst);
		waitKey(0);
	}
}
void main()
{
	org = imread("1.jpg");
	org.copyTo(img);
	org.copyTo(tmp);
	namedWindow("img");//定义一个img窗口
	setMouseCallback("img",on_mouse,0);//调用回调函数
	imshow("img",img);
	cv::waitKey(0);
}