WP_Customize_Image_Control Return Default image

I’m struggling to understand how the WP_Customize_Image_Control returns the default image once a subsequent image has been set. I see how the color picker does this as there is a default button but on the image controller there is only an option to remove the “subsequently-set” image.

The add_settings takes a default parameter and it’s passed to the Customizer admin panel initially but how does it get restored?

$wp_customize->add_setting('logo', array(
		'default' => get_bloginfo('template_directory') . '/img/logo.png',

		$wp_customize->add_control( new WP_Customize_Image_Control ( $wp_customize, 'logo', array(
		'label' => __('Change Logo', 'mytheme'),
		'section' => 'mytheme_images',
		'settings' => 'logo'
		) ) );