If a header image is specified here, it will override the default header image specified in Appearance-Header. It will be displayed for this post or page only. Header images should be at least 1000 pixels wide. A header image will not be displayed for small screens.

the_field('imgurl'); ?> setGroupName('nn')->setInsertButtonLabel('Insert'); ?>

getField(array('name' => $mb->get_the_name(), 'value' => $mb->get_the_value())); ?> getButton(); ?>