CB Gallery is organized into per-user then per-type folders. Image fields are not. Audio, video, and file fields are organized into per-user. CB Gallery folder structure is htaccess secured and does not permit direct access. Image, audio, video, and file fields are not considered secured as they allow direct directory access and are not accessed through PHP specifically like CB Gallery.
CB Gallery has an entire set of access settings and can even have per-media privacy settings via CB Privacy. I suggest taking a look at its addons page below for further details.
www.joomlapolis.com/addons/cb-gallery
Feel free to give it a try on our demo site as well. Tinker with it however you like as it'll reset automatically.
demo.cbdemosites.com/