Using EO.Web Captcha is very similar to using standard ASP.NET validation controls. It supports ValidationGroup property and automatically participate page validation. After placing an EO.Web Captcha control in the page, you can use the following code to determine whether user has entered the correct CAPTCHA code:

//Use EO.Web.Captcha's IsValid property
if (Captcha1.IsValid)
{
    .....
}

//Or use Page.IsValid
if (Page.IsValid)
{
    ....
}

'Use EO.Web.Captcha's IsValid property
If Captcha1.IsValid Then
    ....
End If

'Or use Page.IsValid
If Page.IsValid Then
    ....
End If

Note that you must ensure page validation is triggered beore checking Captcha.IsValid or Page.IsValid. For example, if a 's CausesValidation is set to false, then clicking the button will not trigger the page's validation logic thus will not update Captcha.IsValid.