Enable / Add ReCaptcha in Joomla 2.5 form

If you are looking for adding recaptcha to your registration or contact form in Joomla site to have less spam here is how to do it in Joomla 2.5

Login into admin

Go to Global Configuration

Under 'Site' look for option 'Default Captcha' and change it from 'none selected' to 'Captcha ReCaptcha'

Once done you will have captcha enabled but if you open a form in front end you will be having an error of
"

• ReCaptcha plugin needs a public key to be set in its parameters. Please contact a site administrator.

"

To solve this go to 'Extensions-> Plug-in Manager'
Look for a plug in named 'Captcha - ReCaptcha'

Once you open it you will see to text fields of public key and private key,

now login to 

https://www.google.com/recaptcha/admin/create 

give the URL of your website and it will give you both the keys. Enter them and save and now you will have recaptcha working on your site.