what happens if you browse directly to the WA_ValidationToolkit/WAVT_CaptchaSecurityImages.php file?
in the browser window, replace the page name with "WA_ValidationToolkit/WAVT_CaptchaSecurityImages.php"
for example, if you browse to the page at:
myPage.php
change it to:
WAVT_CaptchaSecurityImages.php
does that show anything in the browser?