Author Image not visible

I really don’t know if this problem has any concern to WordPress version or not. I am trying to add an Author image to its post using ‘Author Image’ plugin to add an image on User profile and following code in content-single.php: <?php echo get_avatar( get_the_author_meta(‘ID’), 60); ?>

I have inserted this code at the bottom of the featured image. The author image is visible if and only if I log-in to my site. But if a visitor is not log-in to my site, the author image is missing like a broken image link.

Please take a look : https://www.khurki.net

Thanks in advance.