Making images from single.php pointing to an attachment .php template

I am trying to make the inserted images from a post (single.php) to point to (single-attachement.php) an attachment page. So far I checked a post here on stackexchange and added this code on the top, before the header of single.php, just that it’s showing me a link to the last image on the page, instead of modifying the structure of the image link.

The result of a shortcode appear BEFORE page content

I have a page, with a shortcode that get all the post from a categorie and put after the content of the page. For no apparent reason, the result of a WP_Query() in the shortcode APPEAR ALWAYS at the top of the page. If i put the shortcode a the top OR at the bottom, the post (3 of them) appear before the content of the page…