DS and theme hook suggestion
I have 3 suggestions:


Might just be a typo on your behalf but the tpl file should be ds-1col--node-article-cartoline.tpl.php rather than ds-1col--node-article-immagini.tpl.php
Could it be that because you've specified ds_1col it's being affected by display suite's naming convention, try using your theme name instead.
There is some sort of inheritance that can be hard to spot, for example to override node--article.tpl.php you need node.tpl.php present in your theme