This article explains about Audio captchas(Completely Automated Public Turing test to tell Computers and Humans Apart) issue. I have chosen this topic because I am scripting PHP registration page with captchas field right now, so I interested in this. This blog post can be useful both for scripter’s and attackers. I think that this topic is relevant to the IT security, because this vulnerability can damage your system.
The captchas designed to prevent automatic filling of the questionnaire. Automatic filling usually use mail spammers, because they need as much as possible email addresses. However, it can be used for other attackers…
Some captchas has voice possibility. It can be helpful for deaf people, but this kind of capthas easier to crack. Newest voice captchas are more secured (with added noise), but it’s helpful not any more.
The audio Captchas cracking system has been develop by a group of researchers at Stanford University. They have developed software called Decaptcha which filters out background noise, separates the likely characters and digits and recognizes them after a training phase with a 50 per cent probability. The university group used various methods and algorithms, which they describe in Link1.