PHP function to import an image from URL into WordPress media library

wp_import_image_from_url.php

<?php

/**
 * Imports an image from URL into media libarary.
 *
 * @param string      $url            The image URL
 * @param string|null $title          The title to use for image in the media library (also will be added as ALT text)
 * @param int         $post_parent_id Post parent ID if applicable
 *
 * @return int|\WP_Error ID of the newly created attachment or Wp_Error object on failure
 */
function import_image_from_url( $url, $title = null, $post_parent_id = 0 ) {
	// sanitize url before processing
	$url = esc_url_raw( $url, array( 'http', 'https' ) );
	if ( empty( $url ) ) {
		return new WP_Error( 400, 'Empty or invalid URL' );
	}
	// fix file name before we start
	preg_match( '/[^\/]+\.(jpe?g|jpe|gif|png)\b/i', $url, $matches );
	/** @var string $name */
	$name = sanitize_file_name( $matches[0] );
	if ( empty( $name ) ) {
		return new WP_Error( 400, 'Invalid file name' );
	}
	// make sure all necessary functions are loaded
	if ( ! function_exists( 'download_url' ) ) {
		require_once( ABSPATH . 'wp-admin/includes/file.php' );
	}
	if ( ! function_exists( 'media_handle_sideload' ) ) {
		require_once( ABSPATH . 'wp-admin/includes/media.php' );
	}
	if ( ! function_exists( 'wp_read_image_metadata' ) ) {
		require_once( ABSPATH . 'wp-admin/includes/image.php' );
	}
	// try to download the image to $tmp location
	/** @var string|\WP_Error $tmp Downloaded temporary file location or WP_Error on failure */
	if ( is_wp_error( $tmp = download_url( $url, 30 ) ) ) {
		return $tmp;
	}
	// construct file data
	$file = array(
		'name'     => $name,
		'tmp_name' => $tmp
	);
	// try to add the description if present
	$post = empty( $title ) ? array() : array(
		'meta_input' => array(
			'_wp_attachment_image_alt' => $title
		)
	);
	// try to upload the image to media library
	/** @var int|\WP_Error $id */
	$id = media_handle_sideload( $file, $post_parent_id, $title, $post );
	// delete the temporary file
	@unlink( $tmp );

	// return the attachment ID or WP_Error on failure
	return $id;
}