[@phkoon]

Thank you, sir

[@BruceYoung]

add_filter( 'manage_posts_columns' , 'by_manage_posts_columns' );
add_filter( 'manage_post_posts_custom_column', 'by_manage_post_posts_custom_column', 10, 2 );
/*
function by_manage_posts_columns( $post_columns ) {
$post_columns['img'] = 'Featured Image';
return $post_columns;
}
*/
function by_manage_posts_columns( $post_columns ) {
$post_columns = array_slice( $post_columns, 0, 1 , true ) + array ( 'img' => 'Featured Image' ) + array_slice( $post_columns, 1, count( $post_columns ), true);
return $post_columns;
}
function by_manage_post_posts_custom_column( $column_name, $post_id ) {
if( $column_name == 'img' ) {
echo get_the_post_thumbnail( $post_id, 'thumbnail' );
}
return $column_name;
}