WordPress has a slight reputation when it comes to spam since the file '/WordPress/wp-comments-post.php' often get's exploited allowing spammers to automate posting to WordPress Blogs. The mess usually costs huge amounts of time to clean up just to go through all the unsolicited junk mail/bogus posts generated.
In an attempt to reduce or eliminate spam coming in through the site I've added the FREE reCAPTCHA plugin for WordPress from recaptcha.net and I'll be evaluating it in the upcoming days to see how well it fights spam coming in through WordPress post comments. Below is a sample of the option that you will see:
CAPTCHA is a term used for Image Verification prior to submitting any sort of data. By asking to interpret an image to read a word it prevents automated software from automatically posting unsolicited junk. By now you probably seen this sort of thing around the web. The way reCAPTCHA differs however is that in this case you will need to type two words instead of just one. More information on reCAPTCHA can be found on the Wiki Page
Sat Jan 5 2008:
Having used the above plugin for a week now, I'm impressed with it and recommend it to anyone having a blog. I see a virtual end of unsolicited/spam posting while legitimate posts are getting through without problems. Kudos to developers of reCAPTCHA.
Sat Dec 13 2008
So far the reCaptcha has done quite well and other then a single bogus user registration, the spam has been cut down to near 0. There is still spam coming in however I have to check to see where it is really coming from as it is not through posting as far as I can see. The remainder of spam is getting caught by the Akismet spam plugin which has been doing a decent job.