How to add a Captcha to your Login form Asp.Net in 10 foolproof steps

A quick and good solution to add Captcha’s to your solution is to use Google’s. There are various solutions available online to make your own captcha, but I prefer using Google’s Recaptcha which can be found on: http://www.google.com/recaptcha

There is this free usercontrol available online.

Here are the 10 easy steps to follow:

1) sign up at https://www.google.com/recaptcha/admin/create

2) add a site

3) copy & paste your public and private key in notepad as reminder

4) download and extract the latest version of the .net control which can be found at http://code.google.com/p/recaptcha/downloads/list?q=label:aspnetlib-Latest

5) put the extracted files in the Bin folder of your solution

6) The next thing is to add a reference in your project to the DLL in your Bin folder. [more]

7) Register the control in the page (or usercontrol) by adding this to the top of the page:

<%@ Register TagPrefix="recaptcha" Namespace="Recaptcha" Assembly="Recaptcha" %>

8) Insert the control in your aspx (or ascx) file at the right place

<recaptcha:RecaptchaControl
    ID="recaptcha"
    runat="server"
    PublicKey="your_public_key"
    PrivateKey="your_private_key"
    />

9) Insert your public and private key which you stored with notepad.

10) Do not forget to validate the Recaptcha control. Here is how I did it in my code behind of an <asp:login control:

protected void Login1_LoggedIn(object sender, EventArgs e)
{
   //LogVisit();
   recaptcha.Validate();
   if (recaptcha.IsValid)
   { // etc

There is more info about this matter available online at http://code.google.com/intl/nl/apis/recaptcha/docs/aspnet.html

You can customize the look and feel of the Recaptcha control with CSS or by using the predefined theme’s, more about that can be found here http://code.google.com/intl/nl/apis/recaptcha/docs/customization.html

I used the blackglass theme like this:

<recaptcha:RecaptchaControl
    ID="recaptcha"
    runat="server"
    PublicKey="my-public-key"
    PrivateKey="my-private-key"
    Theme="blackglass"
    />

Good luck!

Let me know in the comments if you had any troubles with following the above 10 step plan.