Dropbox Carousel allows you to hide a single photo or multiple photo at a time. It will remain safely stored in your Dropbox. Once you hide photos, they will not appear in the Dropbox website's "Photos" tab or in your Carousel gallery. You can restore or delete your hidden photos. To do so, open your "Carousel" app and tap "Menu" i.e "3 horizontal lines" located at the top left corner on the screen. Tap "Hidden Photos & Videos" section and select the option which you want.