add_action('after_setup_theme', function(){
  // 1200x675 (16:9) zuschneiden — anpassen nach Wunsch
  add_image_size('my_featured_size', 1200, 675, true);
});		
		<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /var/www/web29922934/html/wordpress/wp-content/themes/naturespace/functions.php:375) in <b>/var/www/web29922934/html/wordpress/wp-includes/pluggable.php</b> on line <b>1531</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /var/www/web29922934/html/wordpress/wp-content/themes/naturespace/functions.php:375) in <b>/var/www/web29922934/html/wordpress/wp-includes/pluggable.php</b> on line <b>1534</b><br />
<!-- WP Super Cache is installed but broken. The constant WPCACHEHOME must be set in the file wp-config.php and point at the WP Super Cache plugin directory. -->