diff -r 490d5cc509ed -r cf61fcea0001 wp/wp-includes/customize/class-wp-customize-header-image-setting.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/customize/class-wp-customize-header-image-setting.php	Mon Oct 14 17:39:30 2019 +0200
@@ -0,0 +1,51 @@
+<?php
+/**
+ * Customize API: WP_Customize_Header_Image_Setting class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * A setting that is used to filter a value, but will not save the results.
+ *
+ * Results should be properly handled using another setting or callback.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Setting
+ */
+final class WP_Customize_Header_Image_Setting extends WP_Customize_Setting {
+	public $id = 'header_image_data';
+
+	/**
+	 * @since 3.4.0
+	 *
+	 * @global Custom_Image_Header $custom_image_header
+	 *
+	 * @param $value
+	 */
+	public function update( $value ) {
+		global $custom_image_header;
+
+		// If _custom_header_background_just_in_time() fails to initialize $custom_image_header when not is_admin().
+		if ( empty( $custom_image_header ) ) {
+			require_once( ABSPATH . 'wp-admin/custom-header.php' );
+			$args = get_theme_support( 'custom-header' );
+			$admin_head_callback = isset( $args[0]['admin-head-callback'] ) ? $args[0]['admin-head-callback'] : null;
+			$admin_preview_callback = isset( $args[0]['admin-preview-callback'] ) ? $args[0]['admin-preview-callback'] : null;
+			$custom_image_header = new Custom_Image_Header( $admin_head_callback, $admin_preview_callback );
+		}
+
+		// If the value doesn't exist (removed or random),
+		// use the header_image value.
+		if ( ! $value )
+			$value = $this->manager->get_setting('header_image')->post_value();
+
+		if ( is_array( $value ) && isset( $value['choice'] ) )
+			$custom_image_header->set_header_image( $value['choice'] );
+		else
+			$custom_image_header->set_header_image( $value );
+	}
+}