First you have to make the book the right size and ratio with the parameters
pageheight="height in px" and
pagewidth="width in px"
e.g.
pagewidth="1932"
pageheight="1713"
Then you can resize (not scale) the image to the desired size.
If all images are about the same and very similar to the page size, you could use somthing like
<img width="1932" height="1713" src="path to your image" />
or
<img width="1932" keepar="true" src="path to your image" />
which will make the image the desired width and adjust the height so it keeps the aspect ratio.
You then should use something like
minscale="0.25" or even smaller.
Since your images have a high resolution. To enable users with smaller monitors to see the whole image.
And maxscale="1", together with zoomsnap="0.25, 0.5, 0.75, 1.0" and zoomsteps="2"
If you intend to use spreadpages, you have to set the pagewidth half of the image width.
You also could use batchpages, if your images are named accordingly and really all the same in size...
The demo book that is in work will help you also; I just posted some info about how to have a look at the incomplete version:
http://www.megazine3.de/forum/index.php/topic,1197.msg4676.html#msg4676You could give it a try... or wait until it is available ;-)