It doesn’t even have to be an icon. For my digital copies of DVDs, I change the icon to the cover of the DVD by copying the image to the clipboard, doing cmd-I on the file, selecting the icon in the upper left corner and pasting the image in place of the icon. The default view for the folder with all the DVD rips has large icons and black text on a black background to hide the file names (for aesthetics). I miss the old carousel view which would make it feel like flipping through a stack of DVDs to find what I wanted to watch.
I don't remember their names, but there used to be apps that would take a raw cover image and place it in a nicely rendered CD/DVD cover template to produce a pseudophotorealistic cover icon which you could then paste on rips.
The Mac customization scene used to be a pretty vibrant place… you can still see traces of it but it's dwindled over the years.
