You need to add an .ico file to your root folder. This file must be named "favicon.ico". There are several on-line sites that can convert a JPG or PNG image to a favicon; search for "image to favicon".
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .