sxi’s approach is a great one, and Scott is correct about there being a Joomla! bridge available for gallery, but a full gallery may be “overkill” for what you are trying to do.
While I agree that some poorly programmed add-on components can expose your content to unregistered users, the Joomla! “core” has that well sorted, so you can rely on the security of Joomla! articles created with the core content component.
That said, there are several excellent extensions that allow you to easily, embed galleries in content items, which you can then assign to only be viewable by registered/logged-in users.
You might investigate some of these before you jump “full-on” into integrating a full blown Gallery2 integration; they may very well meet your needs and are a lot more lightweight.