Thank you for the answer, Valloric!
This is just an example but I was more thinking about if there would be a button to create simple SVG element e.g.
Code:
<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"
width="100%" height="100%" viewBox="0 0 685 1000" preserveAspectRatio="xMidYMid meet">
<image width="685" height="1000" xlink:href="images/image.jpg" />
</svg>
So the user could easily add a scaling cover for the ebook. But yes, SVG is a huge format. Anyway, keep up the good work!