Make sure that you are using the same cookie container on the post request, also that you are scraping the correct captcha code from the register page on the first request & then calling the image with the same cookies also, then download the image to your hard drive & process within the software / a captcha breaker & then when posting the registration data you will also need to set the fs_signature to the same code & scrape the dynamic fs_ variables beforehand to include with the request.