How to redirect image attachment urls to parent post?

I have seen this question asked before but cannot see an answer that works…

I would like my image attachment urls to redirect to their parent posts…

I have tried:

1) adding this to the first line of image.php but it doesn’t work at all

<?php wp_redirect(get_permalink($post->post_parent)); ?>

2) I have added attachment redirect plugin but that just redirects everything to the homepage.

So… Please can someone advise how I can get image attachments to redirect to their parent posts…