[WordPress] How to add media categories

wp-media-categories.php

<?php
/**
 * Taxonomy for media files.
 */
function init_media_categories() {
	register_taxonomy( 'media_cat', 'attachment', array(
		'label'                 => __( 'Categories' ),
		'hierarchical'          => true,
		'public'                => false,
		'show_ui'               => true,
		'show_admin_column'     => true,
		'update_count_callback' => '_update_generic_term_count',
		'rewrite'               => array( 'slug' => 'media-category' ),
	) );
}

add_action( 'init', 'init_media_categories' );