点击鼠标左键开始画roi，右键或者回车代表画框完毕

并且做了封装。

import cv2
import numpy as np

class ROIDrawer:
    def __init__(self, image_path):
        self.drawing = False
        self.ix, self.iy = -1, -1
        self.roi = None
        self.image_o = cv2.imread(image_path)
        self.image = self.image_o.copy()
        self.temp_image = self.image.copy()
        self.ok=False

    def draw_crosshair(self, event, x, y, flags, param):
        self.temp_image = self.image.copy()
        if self.roi is None and not self.drawing:
            cv2.line(self.temp_image, (x, 0), (x, self.temp_image.shape[0]), (0, 255, 0), 1)
            cv2.line(self.temp_image, (0, y), (self.temp_image.shape[1], y), (0, 255, 0), 1)

        if event == cv2.EVENT_LBUTTONDOWN:
            self.drawing