// Add the posts and pages columns filter. They can both use the same function.
add_filter('manage_posts_columns', 'tcb_add_post_thumbnail_column', 5);
add_filter('manage_pages_columns', 'tcb_add_post_thumbnail_column', 5);

// Add the column
function tcb_add_post_thumbnail_column($cols){
  $cols['tcb_post_thumb'] = __('Featured');
  return $cols;
}

// Hook into the posts an pages column managing. Sharing function callback again.
add_action('manage_posts_custom_column', 'tcb_display_post_thumbnail_column', 5, 2);
add_action('manage_pages_custom_column', 'tcb_display_post_thumbnail_column', 5, 2);

// Grab featured-thumbnail size post thumbnail and display it.
function tcb_display_post_thumbnail_column($col, $id){
  switch($col){
    case 'tcb_post_thumb':
      if( function_exists('the_post_thumbnail') )
        echo the_post_thumbnail( 'admin-list-thumb' );
      else
        echo 'Not supported in theme';
      break;
  }
}

add featured image thumbnail to WordPress admin columns

php, wordpress

PHP