Active Forums has the ability to allow anonymous users to create topics and post replies.  By default, when anonymous users are allowed to create content a CAPTCHA challenge will be displayed.  This is a common way to prevent spam from entering your forums.  In some situations you may want to disable CAPTCHA.  The option to disable CAPTCHA is available from the Community Settings tab under the Settings section of the Active Forums Control Panel.  Select "No" to disable Captcha for anonymous users then click the Save Button.