functions.php

<?php
/**
 * Migrate data from Taxonomy Images plugin to WP Term Images 
 *
 * @author Bill Erickson
 * @see https://www.billerickson.net/code/migrate-taxonomy-images-to-wp-term-images
 */
function be_migrate_taxonomy_images() {

	$taxonomy_images = get_option( 'taxonomy_image_plugin' );
	$meta_key = 'image';

	foreach( $taxonomy_images as $term_id => $image_id ) {
		update_term_meta( $term_id, $meta_key, $image_id );
	}
}
add_action( 'wp_footer', 'be_migrate_taxonomy_images' );