draw a circle over image opencv

Im usign python and opencv to get a image from the webcam, and I want to know how to draw a circle over my image, just a simple green circle with transparent fill

my code:

import cv2
import numpy
import sys

if __name__ == '__main__':


    #get current frame from webcam
    cam = cv2.VideoCapture(0)
    img = cam.read()

    #how draw a circle????

    cv2.imshow('WebCam', img)

    cv2.waitKey()

Thanks in advance.

Answer

cv2.circle(img, center, radius, color, thickness=1, lineType=8, shift=0) → None
Draws a circle.

Parameters: 
img (CvArr) – Image where the circle is drawn
center (CvPoint) – Center of the circle
radius (int) – Radius of the circle
color (CvScalar) – Circle color
thickness (int) – Thickness of the circle outline if positive, otherwise this indicates that a filled circle is to be drawn
lineType (int) – Type of the circle boundary, see Line description
shift (int) – Number of fractional bits in the center coordinates and radius value

Use “thickness” parameter for only the border.