yaCAPTCHA is a CAPTCHA plugin for WordPress that helps you block comment spam from automated bots.
For WordPress version lower than 3.0, you can change the location of the CAPTCHA field within the comment form by changing the location of the 'comment_form' call in your theme's comments.php file. The CAPTCHA field appears at the same location as the 'comment_form' call. The default location for the 'comment_form' call can make it confusing for some people because the CAPTCHA will appear after the submit button. I suggest you change it so that it appears before the submit button. This is not necessary if you are using version 3.0 or a higher version of WordPress.
You can customize the messages that are shown by changing the content of $yaCaptchaCharInputMsg, $yaCaptchaCharNoMatchMsg and $yaCaptchaCharAlternateCaptchaText in the yacaptcha.php file. The default messages should be good enough for most English blogs.
You can customize the HTML code that is used in the comment section to match your theme preferences by changing the code in the yaCaptchaCommentForm function for WordPress version lower than 3.0 and in the yaCaptchaCommentFormAfterFields function for WordPress version 3.0 or higher in the yacaptcha.php file. The default HTML code match the default WordPress theme.
You can customize the image properties like how many characters are shown or which characters are used by changing values in the kcaptcha_config.php file. The default values should be good enough for most people.
The CAPTCHA is not shown and it is not validated for logged in users. It assumes that logged in users are already validated and they will not post spam.
First, make sure that you meet all the requirements. If you are still having problems, you can contact me.