因为图片的链接会在您打开该链接后src为您提供一个随机的 码图片！
src可以从屏幕快照中截取屏幕快照，而不是从图像的上下载文件。但是，您需要下载Pillow（pip installPillow）并按照此答案中提到的方式使用它：
from PIL import Image
from selenium import webdriver
def get_captcha(driver, element, path):
# Now that we have the preliminary stuff out of the way time to get that image :D
location = element.location
size = element.size
# saves screenshot of entire page
driver.save_screenshot(path)
# uses PIL library to open image in memory
image = Image.open(path)
left = location['x']
top = location['y'] + 140
right = location['x'] + size['width']
bottom = location['y'] + size['height'] + 140
image = image.crop((left, top, right, bottom)) # defines crop points
image.save(path, 'jpeg') # saves new cropped image
driver = webdriver.Firefox()
driver.get("http://sistemas.cvm.gov.br/?fundosreg")
# change frame
driver.switch_to.frame("Main")
# download image/captcha
img = driver.find_element_by_xpath(".//*[@id='trRandom3']/td[2]/img")
get_captcha(driver, img, "captcha.jpeg")
driver = webdriver.Firefox()
driver.get("http://sistemas.cvm.gov.br/?fundosreg")
# change frame
driver.switch_to.frame("Main")
# download image/captcha
img = driver.find_element_by_xpath(".//*[@id='trRandom3']/td[2]/img")
get_captcha(driver, img, "captcha.jpeg")
（请注意，我对代码进行了一些更改，因此可以在您的情况下使用。）
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