Sharing protected files and images

You may use referrer whitelist to share protected files between websites or servers but this method will not work for some media types because it requires user-dependent HTTP referrer check.

If you use LINK protection method there is a better solution:

Install HotlinkBlocker on every site that will use protected content and enable LINK protection method. This step is required because HotlinkBlockes will process links on pages only if there is at least one LINK protected folder. You may use @^$ directory pattern on sites that do not have any protected content inside to match nothing.
Then replicate Signature value for all sites that require access to the protected content and add /xxxxxxxxxxxxxxxx/ template to the links as described in LINK protection method. You may also need to synchronize clock to share files between different servers. Now you can link to the protected content from other sites because HotlinkBlocker will sign links there.

But keep your signatures in safe place because if intruder get this private signature it will be possible to generate a valid links to your content for example by using another instance of HotlinkBlocker installed on malicious server. If you lost private signature simply generate new one and share it again.