如何设置Scrapy来处理验证码

I'm trying to scrape a site that requires the user to enter the search value and a captcha. I've got an optical character recognition (OCR) routine for the captcha that succeeds about 33% of the time. Since the captchas are always alphabetic text, I want to reload the captcha if the OCR function returns non-alphabetic characters. Once I have a text "word", I want to submit the search form. I'm trying to scrape a site that requires the u