' . __( 'Recommended image sizes', 'blue-planet' ) . '
'; $content .= '
' . sprintf( __( 'Secondary Slider : %dpx X %dpx', 'blue-planet' ), 720, 350 ); } return $content; } endif; add_filter( 'admin_post_thumbnail_html', 'blue_planet_featured_image_instruction', 10, 2 );