Just something simple like showing an image and asking the user to type in the number on the image.
+7
A:
Take a look at reCAPTCHA. It's free, easy to add and helps a good cause (digitizing books). It's also accessible to the blind or visually impaired.
dF
2008-09-06 16:27:31
Clay Nichols
2008-09-06 20:44:00
A:
I'm sure there are other questions on this site regarding this, but CAPTCHA, in its current conceptualization, is broken and often easily bypassed. NONE of the existing solutions will block 95% of spam - GMail succeeds only 20% of the time, at best.
It's actually probably a lot worse than that, since that statistic is only using OCR, and there are other ways around it. I recently gave a talk on the subject at OWASP, but the ppt is not online yet...
While CAPTCHA cannot provide actual protection in any form, it may be enough for your needs, if what you want is to block casual drive-by trash. But it won't stop even semi-professional spammers.
AviD
2008-09-17 05:17:22
A:
If you dont want to use third party capcha you can create your own its simple in PHP you can see more details here http://www.white-hat-web-design.co.uk/articles/php-captcha.php