Make images private in Wordpress

I'm making a site, that I would like to make private. The most important part, is that the images on the domain can't be seen, without the user logging in first. So I would like all traffic to be redirected to http://ift.tt/1RrbBBI (also for images), if the user isn't logged in.

Here's what I've tried:

1) Plugins. I've tried both Wordpress Force Login , the plugin wp-require-login and a Coming soon page and Maintenance mode.

2) Adding a function from this answer. Which is this:

function is_login_page() {
    return in_array( $GLOBALS['pagenow'], array( 'wp-login.php', 'wp-register.php' ) );
}

function wpse_make_blog_private() {
    if ( ! is_user_logged_in() && ! is_admin() && ! is_login_page() ) { 
    global $wp_query;
    $wp_query->set_404();
    }
}
add_action( 'wp', 'wpse_make_blog_private' );

Non of these things redirects the traffic, if I go to the direct URL for the image (such as http://ift.tt/1Nh1z7r ).

Can that be done?

----------------- EDIT 1 --------------

Mevius pointed out, that Wordpress might not be loaded, if you type in the direct URL to an image, so he suggests, that it should be done on apache-level.

------------- END OF EDIT 1 -----------

via Chebli Mohamed