import cv2 as cv

# 1
img=cv.imread("sample.jpg",cv.IMREAD_GRAYSCALE)
# 2
def draw_circle(event,x,y,flags,param):
    if event==cv.EVENT_LBUTTONDOWN:
        cv.circle(img,(x,y),10,0,-1)
#3
cv.namedWindow('modify_sample')
cv.setMouseCallback('modify_sample',draw_circle)
#4
alpha=0.3
beta=80
while(1):
    cv.imshow('modify_sample',img)
    pressedKey=cv.waitKey(5)
    # 5
    if pressedKey==ord('q'):
        break
    if pressedKey==ord('s'):
        cv.imwrite('modified_sample.jpg',img)