S Hetjens

This plug-in adds the post thumbnail of articles to the RSS and Atom feed via Media RSS (MRSS) specification. Media RSS was 
invented by Yahoo as an extension to RSS feeds used for syndicating multimedia files (audio, video, image). This 
plug-in adds the post thumbnail defined by author of the article to RSS and Atom feeds of the blog. This plug-in 
activates the post thumbnail feature of WordPress, if the theme is not doing it. It is enough to activate the plug-in 
to work, it has no configuration parameters.
MediaRSS is a nice addition to your blog if you want to syndicate your content to other platforms. More and more 
platforms and RSS feed readers support it. The Notes App of Facebook recognize the post thumbnail and displays it in 
every newsfeed item.

Hetjens MediaRSS

This plug-in adds the post thumbnail of articles to the RSS and Atom-Feed via Media RSS specification.

Joen Asmussen

This plugin appends a customizable message with a link to every post in your RSS feed. This can help discourage robots from scraping your content (automatically copying and posting it elsewhere). This is the default message:
<pre><code>[postname] originally appeared on [sitename] on [postdate].
</code></pre>

Anti Feed-Scraper Message

Discourage robots from scraping your RSS feed.

Hetjens MediaRSS vs Anti Feed-Scraper Message