Suppose I am making some manual backups.

In my /home/pictures folder I have lots of subfolders and lots of pictures.

On my backup USB drive, I already have a backup that has SOME of those folders and SOME of those picture files (but not all of them). I also have folders and files from ANOTHER computer in that same backup folder on the USB drive.

So if i want to backup from my desktop again, what would happen if I just grabbed my /home/pictures folder and dragged it over to the D:/backups folder (where the /pictures backup folder resides, with subfolders and pictures from other computers?

1) Will it simply overwrite all the folders, subfolders and files in the /pictures folder?

2) Will it "merge" the folders and files? (i.e., keeping the existing subfolers and picture files in the /pictures folder on the USB drive while ADDING any subfolders and picture files from my home/pictures folder that don'currently exist on the D:/backups/pictures folder?

3) Something else?

Or does it depend specifically on the Distro / Desktop / File manager being used?

I am using Linux Mint 17.3 cinnamon with nemo