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' ) );

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)