KLicheR

Scan your WordPress installation for all missing attachment files, download them from another WordPress installation and resize them with your defined image sizes.
Know that the plugin will not create new media on your installation database, it’ll just use the existings entries of medias in your database to retrieve the physical files on another WordPress installation.
E.g.: http://serverA.com have an entry for the mediaX in his database. The path for the physical file is supposed to be http://serverA.com/wp-content/uploads/2013/06/mediaX.jpg but it’s not here. If you know that this same media exists on http://serverB.com + the physical file, you can use this plugin on http://serverA.com, specifying http://serverB.com in the Server URL field and the plugin will search the file here: http://serverB.com/wp-content/uploads/2013/06/mediaX.jpg. If it find it, it will be downloaded here: http://serverA.com/wp-content/uploads/2013/06/mediaX.jpg.
<h4>Do you need this?</h4>
This plugin is useful if you have multiple instances of a same project installed on multiple servers.
For example, a team of developers, each of them having a copy of the “master” installation located at the production server. Periodically, the database of the “master” installation is given to the developers who update their code through a <a href="https://en.wikipedia.org/wiki/Revision_control" rel="nofollow ugc">VCS</a> (like SVN, GIT, Mercurial). There is chance that the uploads folder is not versionned, which is good, so the plugin is useful here to download the medias from the “master” installation.
<h4>How tu use it?</h4>
In the admin, go to Tools/Import and choose the Attachment files importer. From here, enter the URL of the WordPress installation that contain the physical files of medias and click Import.
Existing files will not be overriden.
<h4>Debug</h4>
The plugin is in an early stage and bugs may occurs. If you want to show a detailled report of the importation process, add this line to your wp-config.php file:
<pre><code>define('ATTACHMENT_FILES_IMPORT_DEBUG', true);
</code></pre>

Attachment Files Importer

Scan your Wordpress installation for all missing attachment files and download them from another Wordpress installation.

Zodan

martenmoolenaar

This plugin allows site admins to protect specific attachment file types (e.g. Pdf, Doc(x)) from direct access. Instead, the files are served through WordPress, allowing you to check if a user is logged in or has the required permissions before granting access.
Features: 
* Adds a checkbox to media attachments to mark them as “Authorized only”. 
* Creates an internal page and rewrite rules to intercept requests to protected file types. 
* Checks user login status (or other custom logic you add) before serving files. 
* Provides a settings page to specify which file types should be protected.
<h3>License</h3>
This plugin is licensed under GPLv2 or later.

Z Authorized Downloads

Protect documents from unauthorized download.

Attachment Files Importer vs Z Authorized Downloads