When you log in to your blog, you will see a “Settings” tab. After clicking on it, you will see a “Comments” link. This link gives you access to the controls you can exert over comments.
Comments—Show or hide. If you readers to be able to leave to comments, choose “Show.” If not, click “Hide.”
Who can comment?—I would recommend that you select “Anyone.” You have other controls that will prohibit inappropriate comments. To limit comments only to those have their own Blogger blog would be a severe limitation on readers.
Enable comment moderation—I would recommend selecting “Yes” on this feature. A box will appear for you to put your e-mail address. When a reader submits a comment, that comment will be e-mailed to you for approval. If the comment is vulgar or consists of spam, you simply do not approve it. The disadvantage would be if you were going to be away from your computer for several days and comments would sit in your e-mail for some time waiting on approval.
Show word verification for comments—This tool is designed to keep spammers from posting to your blog. Readers will see a group of letters. In order to post, they would have to type the series of letters accurately. Word verification ensures that a real person is composing the comment. If you are using the “Comment Moderation” as discussed above, you would not need “Word Verification.”