Maybe sideload an image URL? This function will download an image URL to your media library but it will only do it if the URL hasn't been downloaded before.

maybe-sideload-image.php

<?php
/**
 * Given a URL to an image maybe sideload into the media library
 *
 * @param  string  $url The URL to sideload into the media library
 * @param  string  $name The title to associate with the image
 * @param  integer $associated_post_id The post ID to associate the sideloaded image to
 */
function maybe_sideload_image( $url = '', $name = '', $associated_post_id = 0 ) {
	require_once ABSPATH . 'wp-admin/includes/media.php';
	require_once ABSPATH . 'wp-admin/includes/file.php';
	require_once ABSPATH . 'wp-admin/includes/image.php';

	// Check if the URL has previously been sideloaded
	$media_args = array(
		'post_type'              => 'attachment',
		'post_mime_type'         => 'image',
		'post_status'            => 'inherit',
		'posts_per_page'         => 10,
		'meta_key'               => '_source_url',
		'meta_value'             => $url,

		'no_found_rows'          => true,
		'update_post_meta_cache' => false,
		'update_post_term_cache' => false,
		'fields'                 => 'ids',
	);
	$posts      = get_posts( $media_args );
	if ( ! empty( $posts[0] ) ) {
		return $posts[0];
	}
	$associated_post_id = absint( $associated_post_id );
	$created_post_id    = media_sideload_image( $url, $associated_post_id, $name, 'id' );
	if ( is_wp_error( $created_post_id ) ) {
		$created_post_id = 0;
	}
	return absint( $created_post_id );
}