怎么通过python获取验证码图片？

写使用python PAMIE模块写一个自动操作IE的脚本，但是获取验证码图片时遇到困难，试过使用win32inet.GetUrlCacheEntryInfo从IE缓存读文件，但读普通图片没问题，一读验证码图片就报错：

pywintypes.error: (2, 'GetUrlCacheEntryInfo', '\xcf\xb5\xcd\xb3\xd5\xd2\xb2\xbb\xb5\xbd\xd6\xb8\xb6\xa8\xb5\xc4\xce\xc4\xbc\xfe\xa1\xa3')

求获取验证码相关解决方案：

import cPAMIE
import urllib
import urllib2

def deCaptcha(function, image_source=None):
    """调用 de-captcher API 解析验证码图片

    Args:
        function: str
            balance: 查询余额，
            picture2: 解析图片
        image_source: str，图片源文件

    Returns:
        dict，de-captcher 解析返回信息

        {
            'ResultCode': 0,
            'MajorID': 107,
            'MinorID': 44685,
            'Type': 0,
            'Timeout': 0,
            'Text': 'n7hjks'
        }
    """

    data = {
        'username': 'username',
        'password': 'password',
        'function': function,
        'pict_to': '0',
        'pict_type': '0',
        'pict': image_source
    }
    keys = 'ResultCode|MajorID|MinorID|Type|Timeout|Text'.split('|')
    de_captcher_server = "http://poster.de-captcher.com/"

    if function is 'balance' and image_source is None:
        data.pop('pict')
        opener = urllib2.build_opener(urllib2.HTTPCookieProcessor())
        result = opener.open(de_captcher_server, urllib.urlencode(data))
        return result
    elif function is 'picture2' and image_source:
        try:
            opener = urllib2.build_opener(urllib2.HTTPCookieProcessor())
            result = opener.open(de_captcher_server, urllib.urlencode(data))
            return dict(zip(keys, result.read().split('|')))
        except KeyError:
            return result


def getCaptchaImage(url):
    """获取验证码图片

    Args:
        url: 字符串，图片的网址

    Returns:
        字符串，图片源文件

        fileObj.read()
    """
    pass
    # 求获取验证码图片的方法


browser = cPAMIE.PAMIE()
browser.navigate('http://example.com/')
captcha_image_src = browser.imageGet('image_element_ID').src
image_source = getCaptchaImage(captcha_image_src)

print deCaptcha(image_source)['Text']