I noticed this as well...my fix is to use an SVG wrapper for full page images along with the
vh/vw units for height and width. I also set the
background color - usually to black, but to whatever complements the cover image. That fills in any blank areas around the image. Set the
width and
height coordinates to the actual size (in pixels) of the image.
Code:
<body style="margin:0; padding:0; text-align:center; background-color:black">
<h1 style="display:none" title="Cover"/>
<div style="margin:0; padding:0">
<svg
xmlns="http://www.w3.org/2000/svg"
height="100vh" width="100vw"
preserveAspectRatio="xMidYMid meet" version="1.1"
viewBox="0 0 473 603"
xmlns:xlink="http://www.w3.org/1999/xlink">
<image width="473" height="603" xlink:href="../Images/cover.jpg"/>
</svg>
</div>
</body>