You can easily delete photos from your Dropbox using Carousel. If you want to delete the hidden photo, then you can delete it from the "Hidden Photos & Videos" section which is located in the Settings menu. You just need to select the photos which you want to delete and tap "Delete" button located at the bottom right corner on the screen. Once you have deleted photos, they are gone from Carousel and Dropbox. If you delete photo directly from your Dropbox account using the Dropbox website or desktop application, then it will delete from your Carousel also.