Web Wiz CAPTCHA is written in house for Classic ASP applications.
It does stop spamming bots, but to defeat CAPTCHA allot of spammers these days are real people working in modern day sweat shops where they are paid peanuts to spam websites and as they are real people they get around any CAPTCHA put inplace to stop spam bots.
If your website visitors are finding the CAPTCHA images hard to read you can modify the noise levels colours, etc. to make the codes easier to read, but if you make it too easy then the spam bots will be able to read the CAPTCHA images. The page below has information on customising the CAPTCHA image;
https://www.webwiz.net/web-wiz-captcha/kb/captcha-image-customisation.htm