Add Brands image to archives.

functions.php

add_action( 'woocommerce_archive_description', 'woocommerce_brand_image_custom', 18 );

function woocommerce_brand_image_custom() {
	if ( is_tax( 'product_brand' ) ){
		global $wp_query;

		$category     = $wp_query->get_queried_object();
		$thumbnail_id = get_woocommerce_term_meta( $category->term_id, 'thumbnail_id', true );
		$image        = wp_get_attachment_url( $thumbnail_id );

		if ( $image ) {
			echo '<img src="' . $image . '" alt="' . $category->name . '" />';
		}
	}
}