Best add-on for CAPTCHA in Tell to a friend module?

[ilmarchez]

Hi guys,

I'm experiecing some problems with the tell to a friend feature: it is used to generate thousands of spam emails.
I'd like to add captcha to stop the use of the Tell to friend feature by automaitc scripts.
I've tried the add-on named "captcha_antirobot_registration_1-3.zip" but I think is unsafe since the CAPTCHA has the value in each image filename (example captcha "1234" is validation_1.gif+validation_2.gif etc).

Could you please tell me which is the best CAPTCHA add-on for Zencart to put in the Tell-to-a-friend feature?

Thank you for your support.

[ilmarchez]

Anybody uses CAPTCHA?

[dbltoe]

Google css anti-spam and look at http://www.zen-cart.com/forum/showthread.php?t=166212 as an alternative.