At 7:24 PM -0400 4/25/07, Justin Frim wrote:
Perhaps lightly off-topic, I had to make a quick audio CAPTCHA to
complement a visual one for a web site. I was thinking of having a
server-side TTS system, but that just became too big a can of worms
for the size of the project. I also had the restriction that the
hosting service provider refused to install any machine-code
executables or compile any programs to be installed on their servers.
So instead I used a collection of 95 sound clips, each one being a
recording of an ASCII character spoken out loud, with the file named
as the 2-digit hex code of the respective character. All the PHP
script had to do was concatenate the audio data portion of the
necessary files, then create a new header and send the result as a
single audio file to the user-agent. Worked like a charm. (I
should also mention the audio clips were in IMA-ADPCM format, so a
simple concatenation like that didn't break anything.)
I did a similar thing with this:
http://sperling.com/examples/captcha/
After I write it up, I will be providing the code to the public.
I simply used mp3 files (my own voice) and made all files the same
size. That way, to create a key, I simply loaded the header that
contained the length and then a set number of other files were
appended to that -- the length was always the same.
However, I did run my audio captcha by a couple dozen visually
impaired testers to fix any problems that they might have -- it's
interesting to see what they see.
Cheers,
tedd
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