The code above will presumably give you the image sized to fill the height of the screen. However, if it is narrower than the screen, it will not fill the full width of the screen, and if it is wider than the screen, I'd expect it to be clipped (probably entirely from the right side).
For this sort of thing, I would suggest using a bit of basic SVG. Take a look at the source code for this test page:
http://kinji.gatwood.net/
and use it as a starting point. That's basically copied straight out of my EPUB and Kindle books (except that there are stylesheets in the books, and the books don't include hackish JavaScript workarounds to allow me to use larger images on desktop computers).
If you really want the image to fully fill the screen, just change "meet" to "slice" in the svg tag's preserveAspectRatio attribute. Be aware, however, that if you do that, when shown on a widescreen device in landscape orientation, on most devices, you'll lose almost half of your image, because it will be massively clipped on the top and bottom.
Unless you're working with an unimportant background image, scale-to-fit is almost always the right choice, rather than scale-to-fill.