The most direct way might be to do something along these lines in a custom module:

    function YOURMODULE_node_presave($node) {
  
      if(isset($node->field_image)) {
        $node->field_image[LANGUAGE_NONE][0]['alt']=$node->title;
        $node->field_image[LANGUAGE_NONE][0]['title']=$node->title;
      }
  
    }

where `field_image` is the actual name of the image field you have in your node.