LightRocket Media Manager has been built around the concept of managing content - which means managing who can see your files, who can download them and who can manage contributors and their content.
By default when files are uploaded into your LightRocket Media Manager archive (the 'back end' of your system), they are not available or visible on any public facing interface and are only accessible to an administrator and the person who originally uploaded the files.
As an administrator you can then decide if you want to publish uploaded files which means those files will become visible on the public facing 'front end' of your platform, and could thus be viewed by visitors to your site.
However, even if a file is published this doesn't mean it's accessible to all. You can still protect it by restricting access (either for viewing or for viewing and downloading) to only those with corresponding permissions (which only admins can grant).
And remember no file on LightRocket Media Manager is ever available for download in a hi-res format until you authorise it. So your files are safe!