Most Dukky sites will not need a CAPTCHA included. Adding this field can cause a level of "drop-off" for consumers who don't want to bother with the extra step and should be avoided unless it really is necessary for the success of your campaign. Remember, it can always be added in the middle of the campaign. So we recommend at least starting your campaign without it, so you don't limit your conversion.
Clients who should consider a CAPTCHA are:
1. Those who have previously had issues with spam bots altering the data of their campaigns in the past.
2. Larger companies with a national presence
3. Those with a high-value sweepstakes or prize that would trigger the interest of spammers and "cheaters"
For a better definition:
"CAPTCHA is actually an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart". The term is trademarked by Carnegie Mellon University and was started in 2000, so it’s not been around too long. In reality a CAPTCHA is a program that can generate and grade different kinds of tests that most humans can pass, but computer programs can not pass. The most common one known is the distorted letters and numbers test. A CAPTCHA must be fully automated without any user intervention, which makes it a reasonable option for website owners.
Adding a CAPTCHA program to your site helps provide a reliable method to validate that the information being submitted is from a real, live human and not from some automated program. The use of CAPTCHA is becoming more widespread and is not just on the major websites any longer. A lot of site integration examples can be found in the common website programming languages. " - http://cmrlkr.wrytestuff.com/swa79904.htm