You will get some text-speech utilities and using that you need to make an audio file. When user clicks on audio icon, play this audio file. If you know the characters your CAPTCHA produces, record sound for each character and when requested by the user, combine all the required audio files and produce a single file. This single file can be provided to user. Doing all these won't be trivial. You will be better off with some third party controls which has all these features built-in. Here[^] is one. :)
Navaneeth How to use google | Ask smart questions