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.

P. Chandra

Adds copyright notice at end of articles in full text RSS feeds, with back links to the blog and original article.
A notice gets attached at the bottom of feed articles like this 
Original Article: Title of Article (linked to permalink) 
Copyright Year. Blog Title (linked). All Rights Reserved
Your Blog title is linked to your blog Url. Your article title is linked to the article permalink.
Blog copyright notices are important as your feed gets freely distributed across the web and is republished without permission by RSS scrappers and autoblogs. After using this plugin, now RSS scrappers will link back to your site, which will suggest to search engines that your blog and article was the original source.

Simple Feed Copyright

Adds copyright notice at end of articles in full text RSS feeds, with back links to the blog and original article.

Hetjens MediaRSS vs Simple Feed Copyright