Thanks to Peter Farrell for creating the free and open source Lyla Captcha ColdFusion component to help stop comment spam, and thanks to Brian Rinaldi for instructions and code appropriate for usage in BlogCFC.
Comments now require the guest to type the text rendered in the image into a text field for validation. Soon I will add this to the Contact Me page as well.
To simplify the task for the guest, I create an array of known strings such as company names, well known terms, or other recognizable words, then select one random array item to be passed to the createCaptchaHashReference(String s) method. Yes, this partially weakens Captcha, but I think it should still be very effective.