How can I get the position and draw rectangle using opencv?

Question

I want to get a position when move and click mouse in picturebox. I want to create rectangle in the image window when and where a mouse is clicked.

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Answer 1

In tracking module of opencv-contrib, there is a nice feature of selectROI.

#include 
// selectROI is part of tracking API
#include 

using namespace std;
using namespace cv;


int main (int argc, char **arv)
{
    // Read image
    Mat im = imread("image.jpg");

    // Select ROI
    Rect2d r = selectROI(im, false); // false -> for creating rectangle from 
                                     //          top-left to bottom-right

    // Crop image
    Mat imCrop = im(r);

    // Display Cropped Image
    imshow("Image", imCrop);
    waitKey(0);

    return 0;
}

Use the mouse to select the ROI(region of interest) and then press SPACE or ENTER button. Cancel the selection process by pressing c button.