Hey guys,
Can you tell m that what is use of image verification code , which always use to appear at sign up form and how can we add it to our site???
There questions that are so well known, and so easy to search in Google, that no matter what we do to be helpful, it is always better to do a search first. And this one is one of those questions.
A bit of informatino about image verification code.
In summary, you want them so bots and spammers don’t create thousand of fake accounts and because you want real humans doing real transations. And if a human wants to spam the system… at least it will take them a bit of work by doing it by hand 
About how to implement it… well, this is so broad that again I do suggest to look for info in Google and then come back with something more specific. Basically you program it yourself or if you use a content management system such as Drupal, Joomla or WordPress, you get a plug-in that does the job for you. 