this message is for all users who want to display, using your plugin, the featured image
Actions to do in RSS-generator website (WordPress)
1) Add featured images in all your posts! Obviously!
2) Install "Featured Images In RSS Feeds" (put Responsive 150px as size)
3) Install "Regenerate Thumbnails" plugin. Regenerate all thumbnails
4) Empty all caches
5) http://yoursite/feed has now, as the first image, the featured images 150*x
WP RSS Multi Importer: when add a feed, you must specify "Media Image Number=1"