A
CAPTCHA (an
initialism for "
Completely
Automated
Public
Turing test to tell
Computers and
Humans
Apart", trademarked by
Carnegie Mellon University) is a type of
challenge-response test used in
computing to determine whether or not the user is human. The term was coined in 2000 by
Luis von Ahn,
Manuel Blum, Nicholas J. Hopper of Carnegie Mellon University, and
John Langford of
IBM. A common type of CAPTCHA requires that the user type the letters of a distorted image, sometimes with the addition of an obscured sequence of letters or digits that appears on the screen.
Because the test is administered by a computer, in contrast to the standard Turing test that is administered by a human, a CAPTCHA is sometimes described as a
reverse Turing test. This term is ambiguous because it could also mean a Turing test in which the participants are both attempting to prove they are the computer.
For further information visit the
The CAPTCHA Project
The
Dracon CAPTCHA Visual Flash System below is a combination of PHP Sessions, JavaScript and Macromedia Flash, it doesn't require any special modules installed on the server and while it's
very difficult to break it with
OCR it is
nearly impossible to break it with a
workaround method (flashvars, javascript, sessions) and can't be done with publicly available CAPTCHA breaking tools, requires highly professional customized approach.
This
Flash CAPTCHA script has two versions, one is extremely simple to install and is less secure, but takes
less than 1 minute to install. If you have only a
small web form that is targeted by
spam only thanks to google and other search engines, but there is no reason why to attack your site for a
special purpose, you can choose the simple version because no general tool will break it automatically without extensive tweaking.
The second version is
more secure, can protect against
automatic submissions of your forms, comments, blogs or url submissions and reverse engineering would take a while, if anyone feels like proving it
inefficient.
Update: The third version is
even more secure. Thanks to reports of vulnerability in previous versions the communication and code transaction has been encrypted to prevent packet sniffing from gaining direct access to the security code. There also have been thoughts about
OCR and
XSS style attacks, but that is a different approach requiring
different skills and we will deal with them after a report of success. As before, please feel free to try to
break it with a robot and kindly let us know if you succeeded.
