How to stop the spam ?

[Nagendra Inuguri]

Hi,
Any ideas on how to stop the spam requests for a website. For example, if a website has a registration form that can be submitted. We have to stop the junk requests to this registration page. What are the different ways to acheive this ?
Thanks,
Nagendra.

[Mani Ram]

The most common approach to stop the automatic registrations is to generate an image with some random characters (or random words) that the user must enter correctly into a text box while registering.
Yahoo! follows this approach. Look at this link for an example. The word keeps changing everytime you visit the page and so it becomes difficult for the robots to spam.