Folder poster adding

I read the below info
“Folder artwork can be set by adding a folder.png or folder.jpg file to any folder (1000 x 1500 recommended size)”
I have a main folder named GAME OF THRONES in the root of the Hdd.
All seasons & episodes are directly in that folder.
Game of thrones s01 e01… etc
I want to give a special folder icon to that main folder (GAME OF THRONES) . I dont like the general folder icon.
What must be the name?
FOLDER. jpeg, folder. jpeg or GAME OF THRONES. jpeg
And where should i put it? inside the root of hdd or inside the “GAME OF THRONES” folder

In this case, you would place an image named ‘folder.jpg’ or ‘folder.png’ in the GAME OF THRONES folder.

Thank you James.