How to apply Captcha image correctly

[Varangian]

Hi

I have another question about Captcha.... how should I apply a Captcha
Image on a Web Form correctlly?

Say I have an ASP.NET WebSite.. where should I make the code validity
check?. Should I do it on the Page_Load event or on each click or Event
where I wish to validate that particular?

Thanks!

 

[Varangian]

anyone knows ?