s3 only emulates folders. If you have such structure of files on s3
avatar1.jpg
avatar2.jpg
folder --
avatar3.jpg
avatar4.jpg
one_more.png
last_image.jpg
than you have 6 logical instances on your bucket:
avatar1.jpg
avatar2.jpg
folder/avatar3.jpg
folder/avatar4.jpg
one_more.png
last_image.jpg
I think you are free to create a file "folder" in the root wich will be incompartable with a usual filesystem structure but possible on s3.