Hmm. Think it would cope with $M_2(\mathbb{Z})\tilde m$? Or $M_2(\mathbb{Z})\tilde m$? Or just plain M_2(\mathbb{Z})\tilde m? In principle it might, since recaptcha is crowd-sourced; if I came up with the same LaTeX representation all previous recaptcha users had, all would be fine...

mvc said...

I had one in the Hebrew alphabet once (since these are old books I'm guessing it was in Yiddish). Of course I just clicked 'reload' -- hopefully their algorithms recognize captcha's that no-one's willing to attempt, and reject them from their queue.

Popup said...

I know that this thread is old, but I have to add a pointer to the excellent CRAPCHA -Completely Ridiculous And Phony Captcha that Hassles for Amusement:

http://crapcha.com/

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