Display WordPress' featured image in RSS feed

functions.php

<?php
function FeatToRSS($content) {
    global $post;

    if ( has_post_thumbnail( $post->ID ) ){
        $content = '' . get_the_post_thumbnail( $post->ID, 'large', array( 'style' => 'max-width: 300px;' ) ) . '' . $content;
    }

    return $content;
}

add_filter('the_excerpt_rss', 'FeatToRSS');
add_filter('the_content_feed', 'FeatToRSS');