I have been recently using the digg audio interface to capcha, because its actually easier for me to interpret phrase. Often when viewing the image, there is ambiguity, however listening to the audio, is a lot easier to do. I would be interested to see if there has been much work in the spamming comunity to crack this kind of captcha, but either way computationally it must be very difficult. It would be great to see this kind of captcha software exported as something other sites can implement independant of the core digg code.
For those of you awaiting commenting, i'm hoping to have a solution out next week.
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