Deathbed getting ready for CAPTCHAs

Tags: captcha

CAPTCHA [Completely Automated Public Turing test to tell Computers and Humans Apart] is a ‘challenge- response ‘test that involves a set of wavy shaped letters or words; usually appearing when a person fills a web form. This ensures that the user is a human being and not a bot. 

Although it’s found effective in avoiding spam to a considerable extent, this cannot be considered as a long term solution.

1. Accessibility - Most of the CAPTCHAs ask users to visually recognize and identify a series of letters or symbols. It’s a tough job for people with a perfect sight. Some systems do have an alternate audio version. But experts say both can be attacked by hackers.

2. Not a Turning Test – According to the rules of a Turing test a humans can easily find out a machine that pretends as a person.  But CAPTCHAs differentiate between a human and another machine. A much difficult task, as long as OCR (Optical Character Recognition) is getting advanced day by day.

3. All CAPTCHAs can be cracked - Technologies are getting sophisticated day by day that people have found out methods to crack CAPTCHAs. As a profitable hobby many hackers are involved in the research to develop the most effortless method to hack CAPTCHAS.

Sites like http://www.captchakiller.com/  have methods to ‘automatically translate’ a CAPTCHA image.

4. Difficult CAPTCHAs - Are you in search of the simpler solution to prevent cracking of CAPTCHAs? Make the test more difficult! Something like

• Asirra (Animal Species Image Recognition for Restricting Access - http://research.microsoft.com/en-us/um/redmond/projects/asirra/ ) – This is a ‘human interactive proof’ where the users are asked to identify the photos of cats and dogs.

• Use of images that has to be dragged and placed at a particular spot. (http://www.webdesignbeach.com/beachbar/ajax-fancy-captcha-jquery-plugin ).

• Google’s image rotation CAPTCHA(http://googleresearch.blogspot.com/2009/04/socially-adjusted-captchas.html ) - This requires a ‘client side coding’. Hence the chance of getting hacked is just one in ten.

5. CAPTCHA measures ability – CAPTCHA measures your efficiency in understanding an unreadable set of letters. But computers are already successful in creating certain human abilities, and are sure to improve in future; creating a threat to tests like CAPTCHA that helps in preventing spamming. 

PS – Use of re-CAPTCHA has been suggested as a sensible option by many experts, a positive result cannot be guaranteed fully.

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