captchas for blind?

[Alex Dean]

der.hans wrote:
> Are there audio captchas? If there are, what if the person is vision
> impaired and can't hear the audio file ( I believe audio still isn't part
> of HTML specifications, browser and/or computer might not support sound,
> person might also be hearing impoaried, etc. )?
>   

I have seen audio captchas, but I don't know how they are implemented.  
I think Google had an audio alternative captcha when I registered on 
their site.

If PHP is an option, there is a PEAR package for creating text-based 
captchas.  It substitutes simple math problems for images.
http://pear.php.net/manual/en/package.text.text-captcha-numeral.php

alex