Years ago, I built a book for a friend using what was then the standard SVG wrapper, that looked, for example, like this:
Code:
<svg xmlns="http://www.w3.org/2000/svg" style="max-width:800px; max-height:1200px" height="90%" preserveAspectRatio="xMidYMid meet" width="90%" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" viewBox="0 0 800 1200" > <image alt="" height="1200" width="800" xlink:href="../Images/cover.jpg"></image>
</svg>
which appears at a cursory glance to be the same as you indicate. Unfortunately, in iBooks the images would still split across screens, as per the Apple bug; the SVG wrapper didn't fix it. Placing them in frames like Apple now dictate is supposed to solve the problem. Alas, the way they ask for the images to be coded doesn't make sense if one has both vertical and horizontal images.
So I'm stumped.