I’m sure you have encountered CAPTCHAS before. You might not know them with that name, but they have become a familiar feature of many websites. So, you want to book some tickets for a gig of your favourite band? Do you want to sign up to a new social network? Or simply interested in recovering your lost password? Well, you are more than likely to have used a CAPTCHA.
A CAPTCHA is a way to identify that the request to the services mentioned above (and many others) is not generated by a computer. This usually asking the user to complete a simple test for a human being but harder to replicate by a computer. One such task is character recognition. The text is supposed to be so distorted that a computer might have trouble identifying them, nonetheless a human being would be able to solve the problem in a very straightforward manner.
Recently this has been put to a good use with the use of reCAPTCHA, which is a service that helps digitise printed material. In many occasions the quality of some words is not good and therefore OCR (Optical Character Recognition) software struggles. However, many CAPTCHAS are solved by humans every single day and this is a resource that reCAPTCHA is chanelling. The idea is to send words that the computer is having problems identifying. So, if the computer cannot do it, how does the system know that you have given the correct answer???
Well, you are provided with two words one known and the other one is the word that needs resolving. If the answer for the known one is correct the system assumes that the second one is also correct. The key is that you don’t know which word is which. If many people are providing the same answer to that unknown word, then it is highly likely that it has been identified.
All of this is great, but what is the connection with the mathematically inclined CAPTCHA. Well, recently a friend of mine came across the following CAPTCHA. That is an excellent way to prove that you are not a bot, and that you are definitely a geek! Well done!