OpenCV: draw a rectangle around a region

Question

How can I use OpenCV in Python to draw rectangles around some regions within an image for object detection purposes?

Accepted Answer

Use cv2:

```
import cv2

cv2.rectangle(img, (x1, y1), (x2, y2), color=(255,0,0), thickness=2)

x1,y1 ------
|          |
|          |
|          |
--------x2,y2
```

[edit] to append the follow-up questions below:

```
cv2.imwrite("my.png",img)

cv2.imshow("lalala", img)
k = cv2.waitKey(0) # 0==wait forever
```

Solution