Display Featured Image in WordPress RSS Feed

featured-image-wordpress-rss-feed.php

<?php
//This will prepend your WordPress RSS feed content with the featured image
add_filter('the_content', 'smartwp_featured_image_in_rss_feed');
function smartwp_featured_image_in_rss_feed( $content ) {
  global $post;
  if( is_feed() ) {
    if ( has_post_thumbnail( $post->ID ) ){
      $prepend = '<div>' . get_the_post_thumbnail( $post->ID, 'medium', array( 'style' => 'margin-bottom: 10px;' ) ) . '</div>';
      $content = $prepend . $content;
    }
  }
  return $content;
}