If you are using Android's pre-installed Gallery, then the local thumbnails will not be displayed.
We flag the folder which contains the thumbnails as not being detected by Android's Gallery.
However, if you are using a third-party photo-recognized app, then there's no guarantee that the thumbnails are hidden well. Because these kind of apps are trying to read every photo file in the local storage.
We suggest to manually select off the directory (/xyz.skybox.player/cache/) if you use third-party apps.
Hope this info helps.