The recommendations seem to be something like:
Code:
<svg xmlns="http://www.w3.org/2000/svg" height="100%" preserveAspectRatio="xMidYMid meet" version="1.1" viewBox="0 0 410 686" width="100%" xmlns:xlink="http://www.w3.org/1999/xlink">
<image height="686" width="410" xlink:href="../Images/cover.jpeg"></image>
</svg>
You need to change the dimensions to match that of the image.
In calibre and the Kobo ereaders, this will display the cover image image full screen with no distortion.