CCing Erik since I have seen him try to create an account on labs.

The captcha were generated using a private key which was not filled in the beta mediawiki configuration which caused ConfirmEdit to never match the user input with the captcha that was shown.

I have set $wmgCaptchaSecret in common/wmf-config/PrivateSettings.php to some random key. Then deleted all captcha from /mnt/upload/private/captcha and regenerate the captcha by passing the key to captcha.py.

Command used to regenerate the captcha:

python php-master/extensions/ConfirmEdit/captcha.py \

--wordlist=/usr/share/dict/words \
--font=/usr/share/fonts/truetype/ttf-dejavu/DejaVuSansMono.ttf \
--key=******* \
--output=/mnt/upload/private/captcha \
--count=1000 --dirs=3

Captcha log is in /home/wikipedia/logs/captcha.log :

2012-07-26 09:33:35 deployment-apache32 commonswiki: ConfirmEdit: passed; new account 'HasharCaptcha3'

\O/

My fault, I didn't notice that mediawiki also needed the captcha key when enabling it. Any reason for choosing /usr/share/fonts/truetype/ttf-dejavu/DejaVuSansMono.ttf ?
I had (arbitrarily) used /usr/share/fonts/truetype/ttf-dejavu/DejaVuSans.ttf, i don't know if there's a difference.

I have chosen DejaVuSansMono arbitrarily just like you :-D