CAPTCHAs (Completely Automated Public Turing test to tell Computers and Humans Apart) can protect you and your users from spammers and crackers.
Frankly speaking … user didn’t like ugly looking pictures and which can be easily cracked.
recapcha – I think the new wave of useful captchas is really fascinating.
I used capcha in a project and I found it is very useful.The very important feature I like is audio support and the way it is regenerate.
so if you are visually handicapped… not an issue ! listen the audio and continue………
http://recaptcha.net
http://recaptcha.net/plugins/php/
- Go through the url ,register the domain and you will get a public key or private key .
- Download the recaptcha-php-1.10.zip.
- Include the code and library from reCAPCHA site along with public and private key .
After 10 minutes you have a big smile on your face .
On the http://recaptcha.net you can find plugins and example of code that supports many programing languages.
Love n Luck,
Jigar 
