In an ideal world, we would want to capture as many leads as possible, convert them all into opportunities, then closed deals, and so on and so forth. But the reality is that we live in an age of spam. Spam from competitors, spam from hackers, spam from rogue code.

A major breakthrough in combating web spam is CAPTCHA ("Completely Automated Public Turing test to tell Computers and Humans Apart"), better known as the distorted images of text we are asked to type in say, when signing up for a Yahoo! email address or Facebook account. Essentially, the way CAPTCHA works is by distorting a text image sufficiently so that only humans can decipher it and therefore making it impossible for automated scripts to spam the service.

Given the pervasiveness of click fraud and web spam, some marketers have considered use of CAPTCHA in lead forms. Is the lead form being submitted by a real prospective customer, versus a computer-generated script from a competitor or hacker? The obvious advantage of CAPTCHA is that it is an easy prospect qualification step for weeding out true interest from the noise.

On the flip side, it may introduce an extra unnecessary burden for your prospect which could mean fewer leads (including fewer good leads). You may have wowed a prospective customer with a compelling offer, but that additional split-second required to decipher the CAPTCHA may pose just enough of a barrier for the prospect to change his or her mind. For precisely this reason, after weighing the pros and cons, we at salesforce.com decided not to use CAPTCHA on our lead forms, opting instead to "filter out the junk" on the back-end. We do, however, employ CAPTCHA for developer account sign-ups.

Currently, there aren't any CAPTCHA solutions on the AppExchange, but you can get it for free from the ReCAPTCHA Project run by the Carnegie Mellon School of Computer Science, an early pioneer in developing CAPTCHA.

In general, I recommend CAPTCHA if you fall under one of these categories:

• web spam is a serious problem (over 50% of your leads are junk or you are spammed so much that your service becomes slow)
• you have far more leads than your sales organization can follow up on, and so you wouldn't mind losing a few good leads among the junk
• your offer is very compelling and/or your product has sufficient market power such that prospective customers are more likely to jump through all the hoops instead of dropping out before clicking submit (eg, the Facebook account or Salesforce developer account sign-up examples discussed above)

Otherwise, you are probably better off exploring alternative means of fighting web spam.