get_uploaded_header_images()

function get_uploaded_header_images() {
	$header_images = array();

	// @todo caching
	$headers = get_posts( array( 'post_type' => 'attachment', 'meta_key' => '_wp_attachment_is_custom_header', 'meta_value' => get_option('stylesheet'), 'orderby' => 'none', 'nopaging' => true ) );

	if ( empty( $headers ) )
		return array();

	foreach ( (array) $headers as $header ) {
		$url = esc_url_raw( wp_get_attachment_url( $header->ID ) );
		$header_data = wp_get_attachment_metadata( $header->ID );
		$header_index = $header->ID;

		$header_images[$header_index] = array();
		$header_images[$header_index]['attachment_id'] = $header->ID;
		$header_images[$header_index]['url'] =  $url;
		$header_images[$header_index]['thumbnail_url'] = $url;
		$header_images[$header_index]['alt_text'] = get_post_meta( $header->ID, '_wp_attachment_image_alt', true );
		$header_images[$header_index]['attachment_parent'] = isset( $header_data['attachment_parent'] ) ? $header_data['attachment_parent'] : '';

		if ( isset( $header_data['width'] ) )
			$header_images[$header_index]['width'] = $header_data['width'];
		if ( isset( $header_data['height'] ) )
			$header_images[$header_index]['height'] = $header_data['height'];
	}

	return $header_images;
}