DCIM is an abbreviation of Digital Camera IMages and is the name of a folder that is automatically created on the memory cards within most digital cameras as well as on most (if not all) mobile phones where the user is able to capture and store photographs.
The DCIM folder contains digital photos taken by or stored to the device, however, the folder can also contain various other files associated with the access and viewing of the images within the DCIM folder, including images that were previously stored within it.
The .thumbnails sub-folder is automatically generated within the DCIM folder on an Android based mobile phone by default.
The .Thumbnails folder is hidden from the normal user by default and, generally, the ‘.’ at the start of the folder name within Android indicates that it is hidden.
It is possible to view the folder using a file manager, the phone may contain one by default or one can be downloaded from the Play Store.
First of all, go to your phone file manager and click on the menu icon on the upper right or left it could be anywhere, enable hidden files After that click on( Dcim) folder inside the ‘Dcim’ folder you will see a hidden folder name (.Thumbnails). In my case, I am using a Samsung Smart Phone.
This hidden folder contains all the thumbnails of your videos, photos, and even your apps icons. Deleting this folder won’t make you lose anything on your phone. This (.thumbnails) folder can be up to 3gb+ in size.
After deleting it, click the + icon on your file manager and create a new file. name it(.thumbnail) for it not to create itself again.