Forum Moderators: phranque
Essentially a captcha is not about security, it doesn't have to be 100% unbreakable to be effective. Image captchas have issues when it comes to accessibility, and the commonly used ones are likely to be either breakable, or very difficult for humans to read.
I recommend you look for a trivia-based captcha that allows you to set unique questions for your site. I have no idea how much it may cost though, you may even have to code your own because they don't seem to be all that common.