How to get the captcha when doing a webrequest?

I'm letting my users register an email account, the users just fills in all information in my program and my program will fill the fields. Well not really it makes a POST request with the correct postdata to the correct form/post url.

However the website requires a captcha, I just simply want to show the captcha to my user, he enters the value and then it gets send along with the postdata.

The register page is here: http://register.rediff.com/register/register.php?FormName=user_details

I can just get all image urls from the html but when I copy the url of the captcha image and go to it, it's a different image then开发者_运维问答 the image i copied the url from:

http://register.rediff.com/register/tb135/tb_getimage.php?uid=1312830635&start=JTNG

How do I do this using HttpWebRequest ? I can just grab the html first:

string html = new WebClient().DownloadString("http://register.rediff.com/register/register.php?FormName=user_details ");

Then get the image url but I don't know how to show the same captcha to the user?

Btw it's not for a bot... it's not something automated.. it's just I don't want the user to show the webinterface...

Not really answer, some advice instead:

If you're writing an app client to work with the website, a better approach would be to write a WCF/WebService for the App to interact with directly - this can just refer directly to your BL layer.

If you want the whole app to work on screen scraping then that's a lot of work ahead, and your app will be dependent on the site not being changed.