How to form a file structure for uploaded files through nginx_module_upload?

Question

Nginx

I use the nginx_module_upload module to upload and store images. After that they are given to nginx through image_filter according to this example Fast resize and caching of images The
question is that I don't understand how to correctly form the file structure for uploaded images?
In the nginx_module_upload module, if the directive that allows you to create hashed directories of any level:

upload_store <directory> [<level 1> [<level 2> ] ... ]

But in the config example that returns images, they are all returned by one parameter ($3):

location ~* ^/resize/([\d\-]+)/([\d\-]+)/(.+)$ {
   alias <STORAGE_ROOT>/$3;
   image_filter resize $1 $2;
   image_filter_buffer 2M;
   error_page 415 = /empty;
}

I would like to identify a picture by id and get it through nginx in the way described above. Tell me what are the options for forming a file structure for pictures and identifying them?
And tell me please how many images can be kept in one directory?