I guess no bloggers like to see their images being hotlink in other spam blogs, forums, etc without their authorization. To fight against these image hotlinking, we can set rules in .htaccess but the drawback here is, it would also block images to appear in feeds. Although its solvable, but writing htaccess codes can look complex for any novice users.
Lim Dul of Bahn-spass wrote a plugin for WordPress that helps prevent image hotlinking as easy as installing and activating. It blocks image hotlinking by displaying this following image by default.