What is a CAPTCHA?

No need to start blushing if someone asks you "what is a CAPTCHA?" at the next cocktail party. This article will have you fully prepared, although I wouldn't necessarily recommend mixing with individuals who feel the urge to discuss CAPTCHA's at cocktail parties.

Dummy Captcha Example

In this age of internet transactions from buying cars on Ebay to exchanging ideas on Hotmail, the programming world was confronted with a dilemma. So how do we curb the abuse of our conveniently built interfaces on the net by powerful computer programs programmed by unscrupulous people who just want to take advantage of the profitable possibilities that are tied to our transactions. In other words, how do we know that it is a human being and not a machine trying to make an Ebay account or sign up for Hotmail or enter a website into a manual submission kiosk on a search engine? Quite simply, we use one of the web's many tips and tricks, called a CAPTCHA.

What is a CAPTCHA, and why does it have such a cool name? Well, a CAPTCHA was one programmer's answer to the massive abuse of internet interfaces by programmers who designed programs that can open up infinite amounts of accounts under infinite names just for the use of spamming and scamming. It is quite frustrating to know that so much time and effort was put into programming machines to take advantage of our networks, but no bad deed goes unpunished. Alta-Vista's answer to machines that sign up for email accounts and other web-based accounts and forums was a simple mechanism that sought to test whether or not the person signing up on a given page is really a human. These programs are commonly referred to as "bots" and the particular bots that were bothering Alta-Vista's team were bots that submit URL's to Alta-Vista's database. Back in 1997, Alta-Vista relied on manual submissions from people who would like their site to be included on Alta-Vista's search results. Some unsavory programmers decided that they could take advantage of Alta-Vista by having a bot submit huge numbers of websites automatically and thus compromise Alta-Vista's search algorithms completely. Alta-Vista went about inventing a simple test that could thwart non-human users, and this was coined later as the "CAPTCHA." (Completely Automated Public Turing Test To Tell Computers and Humans Apart)

A CAPTCHA works essentially by synthesizing an image that a human being should be able to read without too much difficulty, while a machine eye will not be able to discern the image. The image is essentially a word that has been stretched and skewed so violently that a human being will still be able to make out what it says, while a computer will not be able to recognize it as more than a group of unrelated pixels. Some CAPTCHAs rely on a huge database of pictures of blurred words which each correspond with the word that is pictured. A human will be able to read the word and enter the term into an input box, and the input of the user will be compared to the value in the database for that particular image. If the input is equivalent to the value in the database, then the interface will assume that the user is indeed a human being and will be allowed to proceed. If the input is not correct, they will be given another image just in case the human reader had trouble discerning that particular CAPTCHA. Obviously, a computer will just get stuck if it cannot read the image. The programmers of these bots were not amused, and they will definitely come back hard.

It is expected that in the coming years, as CAPTCHAs get better at thwarting bots, the bot programmers will get better at building programs and machine "eyes" that can recognize what the human eye can recognize. Obviously, this will require quite a bit of time and effort on the part of these unsavory programmers, but where there is a will, there is a way. Interestingly, it can be assumed that spammers may actually benefit from the advanced OCR (Optical Character Recognition - the term used for technology that recognizes imaging, or computer image recognition software) that will inevitably be made by programmers who need to build a better bot to thwart the CAPTCHA. As for now, we need to just hope that the designers of the CAPTCHA can stay one step ahead of the bot .

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