The word-verification option
To prevent automated software from posting spam comments on your blog, you can ask visitors to enter a short code called a CAPTCHA, before they can post.
Turn on word verification:
- Sign in to blogger.com
- Select "Settings" from the drop-down menu.
- On the left, click Posts and comments.
- Under "Comments," select Yes for "Show word verification." Visitors to your blog will be shown an image of letters or numbers to type to get permission to comment.
With every visual CAPTCHA there will also be an audio version, for visually impaired users. Just click the icon next to the word verification field, and you will hear a list of numbers. Typing these numbers will let you complete the verification step.
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.