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Written by Denize Rodricks

Ever filled out the little word verification tests displayed at the bottom of sign-up forms, and wondered why they were placed there? Well, these tests are a type of CAPTCHA, designed to tell if you are a real human or a machine. Developed in 2000, CAPTCHA code was created to prevent automated spam robots from filling out forms, sending out spam and carrying out other malicious activities.

CAPTCHA is an acronym for 'Completely Automated Public Turing Test to Tell Computers and Humans Apart'. It is a security feature used by a Website, to tell if it is communicating with a human or an automated spam robot. CAPTCHA's are useful in situations where it is absolutely essential to tell humans and machines apart, such as newsletter subscription, online registration, placing orders, filling surveys and e-commerce transactions. Automated bots are usually used to send spam for commercial promotion, but can also be used for malicious purposes like harassment or vandalism. Some of the main applications of CAPTCHA are:

• Prevents bogus comment spam on blogs. This spam is usually sent by unethical SEO companies, to build links that boost the search engine rankings of client websites.
• Protects free email services, like Google, Yahoo and Hotmail, from bots that sign up for thousands of Email accounts every minute.
• Hides your email address from web scrapers that try to collect email addresses, to send out bulk spam.
• Ensures only humans can vote in online polls and surveys.
• Prevents dictionary attacks from bots, which continuously enter words, to break the password of a system.
• Prevents automated software from placing thousands of fake orders for a product or service, on business contact forms.

The most common type of CAPTCHA is the distorted word test. This test presents the user with alphabets and numbers that are twisted out-of-shape to make the images resistant to OCR (Optical Character Recognition). Users need to identify and enter the characters correctly, in the field provided, to complete the submission process. As humans can easily read the distorted text, which are undecipherable by machines, they can be verified as genuine users.

New CAPTCHA Developments

The most common complaint against the distorted word test is that some images were so complex, that even humans could not decipher them. People got tired of having to re-enter different CAPTCHA codes, a number of times, before a website accepted their form submission. Also, blind users, who use screen readers and other tools to browse the Internet, were unable to see the words in the image for the CAPTCHA test. Today, automated spam robots are getting smarter with the development of new technology. The creation of new algorithms, together with OCR, has enabled them to recognize the pattern of characters in images, even on noisy backgrounds. These issues have lead to the development of new systems of CAPTCHA. Some of them are:

1. Angled Line: An angled line, struck through curvy text, makes segmentation and OCR difficult for automated programs.
2. Pictures: Users are presented with a series of pictures, and asked to enter the common element among them or click on a specific picture.
3. Simple Questions: Users are asked simple math or word questions like 'What is 5 + 2?'
4. Sound: An accessibility feature that is useful for blind users, this CAPTCHA plays an audio clip that reads out characters, which users have to enter in a text box.
5. Confirmation Page: A simple thank you page asks users to verify the information they have submitted.

Before you select a type of CAPTCHA for your contact form, check out the various options available, and see which suits your requirements the best. Some offer extremely high levels of spam protection, while others provide accessibility features for people who are disabled. One solution does not fit all websites, so do a bit of research before you select a type of CAPTCHA code for your website.

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