One thing I noticed after adding some media was that while the images look fine for books, which are rectangles, other items, such as CDs, were ending up distorted. I then went back to the Frontend Settings and remembered there was a setting for "media cover size." I had it set as 160/124, which was height and width. So, I deleted the width and left it blank. Now all my media covers have the height of 160, but the width is variable and adjusts appropriately. So now CDs look square. This will also help with other shapes of media, such as wide books.