I didn't enable CAPTCHAs, for commenting on my blog! Why are my readers having to solve one, before commenting?It appears that Blogger has added a new CAPTCHA form, to the commenting process.
In Blogger Help: The word-verification option, we see the notation.
Note: Even if you don't have word verification turned on, anonymous commenters might be asked to enter some text. This helps protect your blog from abuse.It appears that "might be asked" is the key detail, here.