How Do I manually Assign Artwork to folders and videos?

I had an older streamer that I upgraded.

I watch concert videos. So I have a folder for an Artist and that folder will be filled with multiple sub folders with different concerts. I did it this way because for artwork to show up on my previous streamer, I would included a …jpg named folder.jpg and the artwork for that video would show up. I would also do one for the Artist folder so that there would be a picture of the artist.

Some videos are Blu Ray rips so its nice to have the 2 sub folders contain the two folders from a Blu Ray rip

How can I make a folder show up with manually selected artwork. I already tried naming the jpg the same as the artist folder and also tried naming the jpg, folder.jpg and it didnt work.

How are you connected to your server? DLNA, UPnP, SMB, FTP, etc

I am connected by FTP as I thought this was the fastest way to connect to my Synology DJ213j