A captcha is a type of challenge test mostly used in computing to help computer to ensure that the given input is coming from human being only and not bot. This generally needs one server which can generate captcha and check the user output, if it matches with the given captcha. What happens, in the general sense is that alphabets are taken and they are distorted so that it is not easy for software to automatically read it and fill it. However, same is easier for the human to read and do it. Generally, whenever computer does character recognition it does so by three things:
- Removal of background noise.
- Splitting images such that each part contains only one character.
- Identifying character in each region.
Generally, task 1 and 3 are easier for computer to do. So, it is wise to make part 2 tougher so that computers are not able to split because if computer is not able to split then it can’t of course identify the character in each region. Today, if you are designing a dynamic website it is good idea to have a captcha for your website while registering or posting so that bot can’t spam on your website. It is possible to use one of available Open Source Software’s to generate captcha to make your site securer. However, it is not very good idea to completely rely on these softwares as it was reported in 2008 that spammers achieved success rate of 30%, using a bot for solving captcha.