Get post image (WP)

get_post_image.php

<?php

function get_post_image($id, $placeholder_path) {
	$post = get_post($id);
	$content = $post->post_content;
	$regex = '/src="([^"]*)"/';
	preg_match( $regex, $content, $matches );
	if (!empty($matches)) {
		return $matches[1];
	} elseif (get_the_post_thumbnail_url($id)) {
		return get_the_post_thumbnail_url($id);
	} else {
		return "$placeholder_path";
	}
}