TGC Captcha Home

Text-Graphics Character CAPTCHA Home Page

The Text-Graphics Character (TGC) CAPTCHA is a CAPTCHA designed for a low-resolution user interface, namely the dumb terminal.

A CAPTCHA is a Completely Automated Public Turing Test to tell Computers and Humans Apart. They're cool! Go to for more information.

The TGC CAPTCHA Project is a collaboration between Chanathip (Meaw) Namprempre and Matthew Dailey.

Source code to add TGC CAPTCHAs to the OpenSSH client and server, version 3.6.1, can be downloaded here: TGC-Captcha-openssh.src.tar.gz. Note: this code is purely experimental at this point, and is not approved by the Secure Shell (secsh) Working Group or anyone else. By downloading this code, you agree that any loss or damage resulting from the use of this software is your problem, not ours. To install, unpack the archive, read the README, and follow the instructions. You will also need the OpenSSH version 3.6.1 source code, available here.

A short paper, submitted to IEEE TENCON, on the TGC CAPTCHA is also available: A Text-Graphics Character CAPTCHA for Password Authentication.

Asian Institute of Technology

Faculty of Engineering, Thammasat University