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 cPAMIEimport urllibimport urllib2def 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 resultdef 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').srcimage_source = getCaptchaImage(captcha_image_src)print deCaptcha(image_source)['Text']