BOTDETECT

.NET, Java, and PHP Captcha generator. BotDetect is accessible; its source code is available; it works in China; and it does not stalk you around!... BotDetect also provides an audio Captcha alternative to keep websites accessible to people with impaired vision, enabling you to make WCAG and Section 508 compliant websites... Our approach to Captcha security is validated by BotDetect's track record. Since 2004, we have over 3000 paying customers and only a single confirmed case of significant automated Captcha breaking by ordinary spammers.