Simple Captcha solution

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captcha.aspx

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Simple Captcha solution for protecting web forms from non-human submissions. This is how the image would look like:

(click the image for source code)
It looks different every time you reload the page. It can be customized.

Build the method for processing the submission:

protected void Submit_Click(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        // your code here
    }
}

Put the validator event into code:

protected void CaptchaValidator_ServerValidate(object source, ServerValidateEventArgs args)
{
    args.IsValid = captcha.Text.Equals((string)Session["captcha"], StringComparison.OrdinalIgnoreCase);
}

Put the image and input box on the page:

<img runat="server" alt="captcha" align="left" src="~/captcha.aspx" />
<asp:TextBox ID="captcha" runat="server" Width="80" />

Put validators on the page:

<asp:RequiredFieldValidator runat="server" ErrorMessage="*" ControlToValidate="captcha" />
<asp:CustomValidator runat="server" ErrorMessage="*" ControlToValidate="captcha" OnServerValidate="CaptchaValidator_ServerValidate" />

Add the Captcha Image Generator page to your site.