It's hard to say in general terms who owns the copyright for an album cover. My hazy impression is that typically neither the musicians nor the original artist do. It's likely that the record company pays the artist on a work-for-hire basis and retains the copyright themselves. But that may not be true. In the case of Dark Side of the Moon, the original designer and graphic design company own the copyright (Storm Thorgerson / Hipgnosis--documentation here: https://rockpopgallery.typepad.com/rockpop_gallery_news/2007/05/cover_story_dar.html )

I seriously doubt that every review site that includes a picture of the DSOTM cover has asked for clearance. That doesn't mean that a Medium author is free to ignore copyright law or can't be sued for IP violation (even if you're not breaking a law, you can be sued of course). So the safest course would be to avoid including a cover photo (even if you took it yourself) in your Medium (or other) piece. I think you'd be safe (but I'm not an attorney) if you provided a link to a site that did feature the cover, but embedding the image yourself would be risky.