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by Ray DeCosta

Q. What is that weird-looking text that has to be typed into a box before you are allowed to add your comments to a website?

A. Those distorted images (usually of text) are known as a CAPTCHA. This odd acronym stands for Completely Automated Public Turing test to tell Computers and Humans Apart. The "Turing" part of the name comes from a test which was originally designed to see if computers were developing (artificial) intelligence approaching that of a human.

In the case of a CAPTCHA, the intended result is to determine whether or not a human is attempting to access a section of the website. This has become necessary because of the proliferation of automated "bots" or robots which attempt to overload a website creating a "Denial of Service" attack. In other cases, a spammer will attempt to acquire numerous free email accounts at sites such as Google or Yahoo.

A CAPTCHA works by generating a test which humans can solve easily, but current-day software cannot. The program will generate some distorted text and then ask the user to type in the letters or numbers that he sees. A human will have very little trouble passing this test while a computer has no reliable way to determine what letters or numbers have been generated. Other tests may involve having the human select which picture is that of a cat, for instance.

The spammers are fighting back and are beginning to create OCR (Optical Character Recognition) programs to determine what characters to enter in the box.

Published: Courier 5/17/09 - Page 5C