import cv2

def draw_circle(event, x, y, flags, params):
	global center, clicked

	if event == cv2.EVENT_LBUTTONDOWN:
		center = (x, y)
		clicked = False

	if event == cv2.EVENT_LBUTTONUP:
		clicked = True

center = (0, 0)
clicked = False

cap = cv2.VideoCapture(0)
cv2.namedWindow('Test')
cv2.setMouseCallback('Test', draw_circle)

while True:
	ret, frame = cap.read()

	if clicked == True:
		cv2.circle(frame, center=center, radius=50, color=(255, 0, 0), thickness=5)

	cv2.imshow('Test', frame)

	if cv2.waitKey(1) & 0xFF == ord('q'):
		break

cap.release()
cv2.destroyAllWindows()