element = wait.until ( EC.visibility_of_element_located((By.CSS_SELECTOR,'.quc-main .quc-field-captcha img'))) #等待验证码加载完毕
browser.save_screenshot('screenshot.png')
left = element.location['x']
top = element.location['y']
right = element.location['x'] + element.size['width']
bottom = element.location['y'] + element.size['height']
im = Image.open('screenshot.png')
im = im.crop((left,top,right,bottom))
im.save('screenshot.png')