Recaptcha is the plugin which we can use in our application to generate a captcha. The recaptcha settings can be done in our system and can be used using the localhost.
But, when we tried to host the same application to any server with the same pair of keys, it will not generate an error but, it will display like "input error - invalid referer" instead of captcha in our form.
Because, when we are getting the pair of keys from google api, we will specify the domain name there. In that, to use those keys in our local system, we will enter domain as "localhost". But, these pair of keys will not work when we deploy that application in any server.
So, for the application to work in the remote host, we should get the pair of keys from google api with the domain name, where we are going to deploy our application. And use them in our application.
So, it will work perfectly this time.
Note:
We can have a new pair of keys for recaptcha using following link:
http://www.google.com/recaptcha/whyrecaptcha