CAPTCHA is a technology created in part at Carnegie Mellon University. It has many uses. It stands for:
Turing test to tell
Relevant to form e-mail, what it does is presents to the visitor a somewhat obscure graphic but legible to human as a piece of code made up of various letters and numbers. Computers likely will not be able to read but most people should have little difficulty. Before the form can be submitted, the visitor needs to input the correct code, as displayed. Therefore, the end result is that the form submission are likely from those of humans. Whether or not they are non-spam is another question. Check out the Captcha Project.
CAPTCHA is not completely secured
There are various techniques publicly available to defeat CAPTCHA. Also, if spammers discover the whereabouts of your mail processing script, CAPTCHA can be bypassed.
The idea here is not to provide a completely secured way to implement form to e-mail solution, but to provide enough of a deterrence so that the cost-benefit of spammers trying to defeat a form is in our favor.
Drawbacks of using CAPTCHA
Please be aware that with the distortion of characters or extraneous markings, people with learning disabilities, particularly dyslexia, can have difficulty deciphering what the actual characters are. Likewise, with poor color contrast, those individuals with color blindness or low vision can also have difficulty getting past the CAPTCHA step. So if your visitors are made up of some of these individuals, you will need to consider it carefully before using this technology.
If you’re interested in setting up CAPTCHA on your website, please click HERE for instructions.