Thanks for the example. I noticed that in your example you didn't specify the width of the image -- is this because you want the image to display at its true "natural" size on the screen?
In my case, I want images which have a high resolution but display in a small space, allowing the user who zooms in to truly see more detail.
Unfortunately, (as far as I know) in order to size images in iBooks you must put the <img> inside a <div> or similar wrapper, then size the <div>. Apparently iBooks ignores size specifications in <img>. (See Liz Castro's post
here.)
Somehow, in these situations I end up with most of my images not zooming. Not sure why. I haven't worked on this issue for a while, but I'd still appreciate any suggestions or input.