I've been fighting this problem myself when trying make prototype ePub documents.
We write our documents mostly in Word and then send them out for printing. They are full of screen shots!
So here are our work arounds to publish for portable devices or laptops or home machines.
Pages is buggy; even Apples ePub template has quirks in it.
(1). If we start the document in Pages and EXPORT it as a pdf AND be certain to select SAVE HIGH RESOLUTION image option when it is exported the final document looks grand AND the pages will magnify when you double click on the page. The images will scale up along with the page BUT how grainy they appears depends on their original size and resolution. This is what we need on iPads an other iOS devices.
(2). If we write the document in Word (Windows) then we need to fool with Word's pdfs settings when we save the document. We are still trying to find the correct options. The extra problem here is how we get the screen shots that we need. Some of use PRINT SCREEN and then copy into MS Paint and copy it into the Word document via the clipboard (cut and paste). Some of use SnagIt and just copy the image into Word from the Clipboard (cut and paste). Some of us convert the image in SnagIt to JPEG or PNG and then insert the image.
Most of the time either option works reasonably well when the document is saved as a pdf. Naturally small images don't magnify well.
(3) We take the document from option (2) and open it in Pages. Some formatting is lost and we need to be careful of font substitution. Now we share/export the document with the high resolution image option selected. The document scales well in iBooks and the images seem to retain their clarity when magnified. This seems to work better than simple saving the original document as a pdf from Word.
(4). Use the ePub format. This makes everything easier for everyone. We don't need to worry about what machine our readers are using to read our documents. If our readers have iBooks then any audio or videos that we embed will work and URL's will launch their web browser. (I haven't tried other ePub applications like Nook or Kindle. The Firefox eBook plug-in will read the book but no audio or video will work.)
There are problems doing this with Pages.
- Sometimes the formatting is lost in conversion and text and images aren't in the correct place.
- Pages has a size limit of about 11Mbytes per chapter which is very easy to exceed with high res images and videos and audio.
- This is the worst problem. The images do not magnify well. They look fuzzy. We can't have this. An image must enlarge clearly.
Summary.
For documents that will not need frequent revision or very important projects that need audio, video, URLs or need precise layout, we are going with Adobe InDesign.
For normal everyday use we are still sticking with Word exporting to pdf.
But we are still trying.
I hope that this helps and thank you for explaining Pages image size quirks. I'll look for them in the manual!