本例子使用了opencv3.0，利用滑鼠選擇矩形框，然後對選擇的區域進行跟蹤

//---------------------------------光流法對特定區域進行跟蹤-----------------
#include <iostream>
#include <opencv2/opencv.hpp>
#include <opencv2/video.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/core/core.hpp>
 

#include <cstdio>

using namespace std;
using namespace cv;

//------------------------------------【全域性函式宣告】------------------------------
void tracking(Mat &frame,Mat &output);
//-------------------------------------【全域性變數宣告】-------------------------------
string window_name = "flow tracking"
 
;
Mat gray;                                                  //當前幀圖片
Mat gray_prev;                                             //預測幀圖片
Mat image;
vector<Point2f> points[2];                                 //point0為特徵點的原來位置，point1位特徵點新的位置
vector<uchar> status;                                      //跟蹤特徵的狀態，特徵的流發現為1，否則為0
 

vector<float> err;
Rect selection;
Point origin;                               //定義原點，
Point pointCentral;
bool selectObject = false;
int trackObject = 0;

static void onMouse(int event,int x,int y,int ,void*)
{
    if(selectObject)
    {
        selection.x=MIN(x,origin.x);
        selection.y=MIN(y,origin.y);
        selection.width = abs(x-origin.x);
        selection.height = abs(y-origin.y);

        selection &= Rect(0,0,image.cols,image.rows);     //保證selection在畫面的裡邊
    }
    switch (event)
    {
        case EVENT_LBUTTONDOWN:
            origin = Point(x,y);
            selection = Rect(x,y,0,0);
            selectObject = true;
            break;
        case EVENT_LBUTTONUP:
            selectObject = false;
            if(selection.width > 0 && selection.height > 0)
            {
                trackObject = -1;
            }
            break;
    }
}


int main() {
    Mat frame;//定義視訊幀
    Mat result;//定義結果
    VideoCapture capture(0);                       //讀取視訊
    if(capture.isOpened())                                 //如果視訊開啟成功，則進行以下步驟
    {
        while(true)
        {
            capture>>frame;                                //讀取當前視訊幀到frame中
            frame.copyTo(image);
            setMouseCallback(window_name,onMouse,0);
            if(!frame.empty())                             //如果當前幀不為空
            {
                tracking(image,result);                    //呼叫定義的函式，開始跟蹤
            }
            else
            {
                cout<<"沒有視訊幀";                          //否則報錯
                break;
            }
            int c = waitKey(50);                           //每隔50ms重新整理一次
            if((char)c == 27)                              //使用者在50ms以內按下“esc”這個按鍵，則跳出迴圈
            {
                break;
            }
            switch (c)
            {
                case 'c':                                  //停止追蹤
                    trackObject = 0;
                    break;
                default:
                    break;
            }
        }
    }
    return 0;
}

void tracking(Mat &frame,Mat &output)
{
    cvtColor(frame,gray,COLOR_BGR2GRAY);                   //將當前的視訊幀轉換為灰度圖，儲存到gray中
    frame.copyTo(output);                                  //拷貝當前幀到輸出output中
    if(selectObject)
    {
        rectangle(output,Point(selection.x,selection.y),Point(selection.x+selection.width,
                                                              selection.y+selection.height),Scalar(255,0,0));
    }
    //滑鼠擡起時，進行檢測
    if(trackObject == -1)
    {
        //選取selection區域的中心點為初始點
        pointCentral = Point(selection.x+selection.width/2,selection.y+selection.height/2);
        points[0].push_back(pointCentral);

        if(gray_prev.empty())
        {
            gray.copyTo(gray_prev);                            //如果前一幀為空，則複製當前幀到前一幀
        }
        if(points[0].size() == 0)
        {
            cout<<"這裡錯了；額"<<endl;
        }
        calcOpticalFlowPyrLK(gray_prev,gray, points[0],points[1],status,err);
        //繪製跟蹤框圖，以point【1】為中心，與selection的長和寬相同的矩形
        rectangle(output,Point(points[1][0].x - selection.width/2,points[1][0].y+selection.height/2),
                  Point(points[1][0].x + selection.width/2,points[1][0].y-selection.height/2),Scalar(255,0,0),3,8,0);
        //畫線，在output影象上，點initial[i]到點points[1][i]的直線段，顏色為（0，0，255）
        line(output,points[0][0],points[1][0],Scalar(0,0,255),4,8);
        //畫圓，在output影象上，圓心為point[1][i],半徑為3，圓的顏色為（0，255，0）
        circle(output,points[1][0],6,Scalar(0,255,0),-1,8);

        swap(points[1],points[0]);                             //交換特徵點容器points[0]和特徵點容器points[1]
        swap(gray_prev,gray);                                  //把當前幀的影象賦值為上一幀影象，以便傳入下一次迭代的calcOpticalFlowPyrLK
    }
    imshow(window_name,output);                            //在視窗window_name展示輸出的結果
}