Have a blog? You will almost assuredly get comments. Unfortunately, many of these comments will be from supposed pharmaceutical companies, personal enhancement firms and numerous get rich schemes. To give you an example, this morning I "cleaned out" the spam comments that had accumulated on the blog over the weekend (over 200 spam comments were deleted). Tonight - a mere 12 hours later nearly 60 more spam comments had been added. 

Spam comments make you look bad and can easily be considered offensive to your blog readers. So what is a blogger to do?

I'm glad you asked.

There is a simple solution that is supported on all major blog platforms, re-captcha keys. A re-captcha key is:

reCAPTCHA is a free CAPTCHA service that helps to digitize books, newspapers and old time radio shows. Check out our paper in Science about it (or read more below).

A CAPTCHA is a program that can tell whether its user is a human or a computer. You've probably seen them — colorful images with distorted text at the bottom of Web registration forms. CAPTCHAs are used by many websites to prevent abuse from "bots," or automated programs usually written to generate spam. No computer program can read distorted text as well as humans can, so bots cannot navigate sites protected by CAPTCHAs. 

For additional information go to http://www.google.com/recaptcha

I installed re-captcha in about 2 minutes and that included the time it took me to get the free code from their site. Simple and effective.

Now, when someone goes to leave a comment on the blog they are presented with a simple question that only a human could answer. The re-captcha inquiry looks like this:

Simple and effective, my comment spam will be virtually eliminated. As a side benefit, by having readers take just a moment to complete the re-captcha inquiry, we are all helping to digitize books.

What is your favorite way to stop comment spam?