Echo the featured image of page assigned to blog in index.php
when a page is set to be the posts page, then the ‘page_for_posts’ option will contain the page id of that page; in this case, you can output the featured image with: if( is_home() && get_option( ‘page_for_posts’ ) echo get_the_post_thumbnail( get_option( ‘page_for_posts’ ) );