def setMouseCallback(
windowName,     #窗口名称
onMouse,      #鼠标响应处理函数
param=None)     #处理函数的ID

event：
EVENT_LBUTTONDBLCLK = 7     左键双击
EVENT_LBUTTONDOWN = 1      左键点击
EVENT_LBUTTONUP = 4       左键释放
EVENT_MBUTTONDBLCLK = 9     中间释放
EVENT_MBUTTONDOWN = 3      中间点击
EVENT_MBUTTONUP = 6       中间释放
EVENT_MOUSEHWHEEL = 11     滚轮事件
EVENT_MOUSEMOVE = 0       滑动
EVENT_MOUSEWHEEL = 10      滚轮事件
EVENT_RBUTTONDBLCLK = 8     右键双击
EVENT_RBUTTONDOWN = 2      右键点击
EVENT_RBUTTONUP = 5       右键释放


flags:
EVENT_FLAG_ALTKEY = 32     按Alt不放事件
EVENT_FLAG_CTRLKEY = 8     按Ctrl不放事件
EVENT_FLAG_LBUTTON = 1     左键拖拽
EVENT_FLAG_MBUTTON = 4     中键拖拽
EVENT_FLAG_RBUTTON = 2     右键拖拽
EVENT_FLAG_SHIFTKEY = 16    按Shift不放事件

import cv2
def draw_rectangle(event,x,y,flags,param):
  global ix, iy
  if event==cv2.EVENT_LBUTTONDOWN:
    ix, iy = x, y
    print("point1:=", x, y)
  elif event==cv2.EVENT_LBUTTONUP:
    print("point2:=", x, y)
    print("width=",x-ix)
    print("height=", y - iy)
    cv2.rectangle(img, (ix, iy), (x, y), (0, 255, 0), 2)

img = cv2.imread("max.png") #加载图片
cv2.namedWindow('image')
cv2.setMouseCallback('image', draw_rectangle)
while(1):
  cv2.imshow('image', img)
  if cv2.waitKey(20) & 0xFF == 27:
    break
cv2.destroyAllWindows()

point1:= 254 64
point2:= 708 569
width= 454
height= 505