CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart," and I use them on my blogs. Whether or not you choose to use them on yours is a different matter.
What is a CAPTCHA?
It's that annoying little gizmo that asks you to retype a random series of numbers and letters into a little box, to show that you're human and not some spamming computer. They even have a little audio icon, so you can hear the series if the scramble is too hard to read (which lots are, I've noticed).
There are different kinds of CAPTCHAs, with differing levels of complexity. Older ones are nicer and less problematic than the later versions.
Should You Use CAPTCHAs on Your Blog?
I do. Some don't: they argue that the balance between Spam-Fighting and making their blogs comment-friendly means not having a CAPTCHA. They worry that a CAPTCHA costs them comments.
Personally, I think it depends on the blogging platform - not all CAPTCHAs are the same. Check yours out. If it's a problem, then consider pulling it.
For example, Typepad (a popular blogging platform) has CAPTCHAs that bother me. One writer-friend loves Typepad, and I like to comment on her blog every once in a while. However, I'm doing this less and less because it's such a hassle. What's going on?
There's an added burden to her CAPTCHA of requiring me to sign in via one of my social media accounts before I can leave a comment. Time-consuming. That alone stops me. And this is a friend: what if I don't want the blogger to know who I am, because I'm worried about uninvited enewsletters, etc.? Anonymous commenting is not only faster for me, but protects me from this mess.
What about Anonymous comments? That's for a different post on a different day.