What have you changed? What updates to the CAPTCHA do you think aren't working?
Add a second one to the page, or play around with it on a new page to see how it works.
That will give it the default values. Then try changing them. Try:
To make it update from a global you would do:
<img src="WA_ValidationToolkit/WAVT_CaptchaSecurityImages.php?bgcolor=<?php echo $WAGLOBAL_Captcha_BG; ?>">
and now the value would come from WAGLOBAL_Captcha_BG. You can remove the globals and add the code inline if that is easier for you, or add more globals to handle more of the available configuration options.
If you find one that doesn't work the way you would expect, copy and paste the resulting <img> tag by viewing the source code on the resulting CAPTCHA image. I will be able to use that to reproduce the problem and I can try to help from there.