Source

File: wp-includes/post.php

function wp_get_original_image_url( $attachment_id ) {
	if ( ! wp_attachment_is_image( $attachment_id ) ) {
		return false;
	}

	$image_url = wp_get_attachment_url( $attachment_id );

	if ( empty( $image_url ) ) {
		return false;
	}

	$image_meta = wp_get_attachment_metadata( $attachment_id );

	if ( empty( $image_meta['original_image'] ) ) {
		$original_image_url = $image_url;
	} else {
		$original_image_url = path_join( dirname( $image_url ), $image_meta['original_image'] );
	}

	/**
	 * Filters the URL to the original attachment image.
	 *
	 * @since 5.3.0
	 *
	 * @param string $original_image_url URL to original image.
	 * @param int    $attachment_id      Attachment ID.
	 */
	return apply_filters( 'wp_get_original_image_url', $original_image_url, $attachment_id );
}