Protecting uploads not working

I am trying to build a private site. One of the most important aspects of the site consists in the uploads, and they definitely need to be private.

I found a very interesting topic on that here: How to Protect Uploads, if User is not Logged In? but it is impossible for me to comment / answer because I am newbie on this forum (1st question btw). Therefore, I post my question in this new topic.

The thing is that this solution does not work for me, and I do not know why. For the moment, I am trying my website on my computer, with an apache server. I put my .htaccess just here:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} -s
RewriteRule ^wp-content/uploads/(.*)$ dl-file.php?file=$1 [QSA,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

and the dl-file.html, as given here: https://gist.github.com/1552239

my uploads are located either just under /wp-content/uploads or in a subdirectory of this directory. I would like to know if there is a way of diagnosing, or see where the does the problem come from. I have deactivated all the plugins, in vain.

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And the culprit was… my apache config. Please do not forget to edit the apache configuration in /etc/apache2/apache2.conf and add the lines

<Directory /var/www/html/>
    AllowOverride All
</Directory>

I still have a question. It seems (but it may be related to the fact that the site is still in localhost) that this method does not prevent from downloading using curl for instance. Am I right?

Thanks.