api security question
 

i'm working on little captcha project and yesterday i've added TTS feature, but now i'm starting to think that might be a bad idea.
I'm using google's TTS api for now. Requests for audio files are routed trough my server, so end user can't see what text is being requested, but they do get audio itself.
test verion is here: http://photocaptcha.us/demo.php
How big security issue that is in your opinion?
obviously i'm thinking about speach recognition software.