WordPress at a glance
function is not described

is_random_header_image() WP 3.2.0

Check if random header image is in use.

Always true if user expressly chooses the option in Appearance > Header. Also true if theme has multiple header images registered, no specific header image is chosen, and theme turns on random headers with add_theme_support().

No Hooks.

Return

true/false.

Usage

is_random_header_image( $type );
$type(string)
The random pool to use. any|default|uploaded
Default: 'any'

Code of is random header image: wp-includes/theme.php VER 5.1.1

<?php
function is_random_header_image( $type = 'any' ) {
	$header_image_mod = get_theme_mod( 'header_image', get_theme_support( 'custom-header', 'default-image' ) );

	if ( 'any' == $type ) {
		if ( 'random-default-image' == $header_image_mod || 'random-uploaded-image' == $header_image_mod || ( '' != get_random_header_image() && empty( $header_image_mod ) ) ) {
			return true;
		}
	} else {
		if ( "random-$type-image" == $header_image_mod ) {
			return true;
		} elseif ( 'default' == $type && empty( $header_image_mod ) && '' != get_random_header_image() ) {
			return true;
		}
	}

	return false;
}