I am having this problem too. I didn't have to add the strtolower as it was already there. I find that the security question will accept 'monday' but not 'Monday'. As a workaround is it possible to remove the 'days' question from the WAVT_CaptchaSecurityImages.php file? If so, I'm not quite sure what to delete as I don't want to muck up the code and make it even worse.