Objective Captcha

By Darko Obradovic from Kaiserslautern.pm
Date: Wednesday, 29 August 2007 12:35
Duration: 20 minutes
Target audience: Any
Language:

Many internet sites have a vital interest to keep bots and crawlers away, be it to preserve a social integrity or to prevent a business from being abused. A Captcha is a popular method for accomplishing this task.

Today's captchas are almost exclusively based on skewed text characters, which is very convenient for human users. However, this method is threatened more and more by the intensive research and progress made in the field of OCR (Optical Character Recognition).

In order to increase security and offer an alternative, We developed a new captcha technique in Perl, based on object recognition. Using the GD module and a pluggable architecture, we present the user with a number of runtime algorithmically generated images, highly variable in appearance.

We present the architecture of the system, explain how to use it on your site, and introduce to the generation of your own objects.

We then discuss the possible vulnerabilities of the approach against image recognition algorithms and measures to be taken against that in the plugins.

We finish with a few interesting points of today's Captchas in general.