It’s not just a walkman. If you want nice consistent-looking album covers on just about any player, desktop or device-based, they need to be square.
I’m shopping around for a new player for my phone. Any player that insists on displaying square artwork only, gets uninstalled real quick. If it can’t handle this, then I’m not interested:
1000x1000px is plenty for a CD cover. They’re usually printed at around 150 lines per inch. A booklet is about 4.5 inches tall, so that would be 675x675px of information. If you need to capture the image and not the screen pattern, descreening and resizing to1000x1000px does the trick really well. The loss of detail is negligible.
CD booklets and record sleeves are pretty close to square. Personally, I prefer to crop them. Digipak covers are a different matter.
But what if that image were wide instead of tall? Really, though, I’m thinking of when lots of images are displayed together, the “album covers” view that many players have.
Anyway, I’m not arguing against having actual dimensions represented, I’m just saying the reason people are attached to square images is probably for consistency and simplicity.