Filter is use to allow / disallow photo tagging. Add the following code in your theme's functions.php file to disallow all users to tag each other into media.
add_filter('rtmedia_can_user_tag_photo', 'rtmedia_filter_can_user_tag_photo', 10, 2);
function rtmedia_filter_can_user_tag_photo($allow, $media_id){
$allow = FALSE;
return $allow;
}