I was on Aljazeera Arabic’s website the other day and, as I was voting on a poll, was presented the following screen:

The CAPTCHA in the screen above immediately caught my attention. The distortions in it seemed very simple, the text was not warped in any form and no overlap between characters.

The following is a URL for one of the CAPTCHAs:

http://www.aljazeera.net/Sitevote/SiteServices/
Contrlos/SecureCAPTCHA/
GenerateImage.aspx?Code=EANmyyXghpajFhOX6rCRKQ==&Length=4

Opening the URL above and refreshing the page a few times gives the following CAPTCHAs:

The dashed grey lines are randomized, while the letters in the CAPTCHAs above are static. The letters are encoded in the Code parameter in the URL. Notice that there are two forms for each character; a straight form and another that is slightly rotated.

Aljazeera’s CAPTCHA can easily be broken by doing the following:

1. Removing the dashed grey lines
2. Finding the characters in the image
3. Separating the characters in the image
4. Classifying each character

I’ll be using Octave/Matlab for the above tasks and will be explaining my algorithm using the following CAPTCHA as an example.

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Following up on my previous post on the El-Tetris algorithm, a Tetris player that clears 16 million rows on average per Tetris game, I thought I would provide an implementation, rather than just a description of the algorithm.

This algorithm is implemented fully in Javascript and the rendering is done in HTML5 canvas. The rendering is purely for cosmetic reasons (so you can actually see how the game is progressing). If you’re only interested in the final score, you can choose to speed up the game by enabling “Hardcore Mode”. In that mode, rendering the board will be disabled and the algorithm will run continuously in the background. You can also change the size of the board; the smaller the board, the shorter the game.

Full source code can be found here.

Note: For faster execution, use Google Chrome.

For the past few months I have been involved with the project BigBlueButton, an open-source web conferencing system. That, along with looking into Etherpad’s source code, really ignited my interest in real-time collaboration technologies.

I started an open-source project to extend BigBlueButton with real-time document collaboration to the conference’s participants. The project is still at a very early stage, but will be out for beta testing in the next release of BigBlueButton.

Before I start ranting about the project, which I am tentatively and temporarily calling it “Live Notes”, let me first show you a demo. Read more