This was posted elsewhere but is useful information in this thread as well.
The maximum (and practical i.e. everyday use) resolutions for the ETI/Gemstar devices are as follows:
EBW 1150: Max usable: 319 x 446; Practical size: 315 x 440; Screen: 320 x 480
REB 1200: Max usable: 472 x 595; Practical size: 468 x 590; Screen: 480 x 640
SOURCE: The Gemstar Formatting Standards.pdf (in appendices) and from practical experience.
Also, for what it's worth:
REB 1100: Max usable: 312 x 472; Practical size: 310 x 468; Screen: 320 x 480
SOURCE: The 'common.py' python module in PDFRead 1.8.1 and from practical experience.
Sometimes when the image used is longer than wider, it will bleed into the bottom (or get "cut off") depending on its aspect ratio. This situation can only be fixed by re-sizing the image to the device's dimensions or inserting width/height specifications within the <img> tag.
Either way you loose the generality of the code and need to re-do this resizing for the other .IMP devices (REB1200/REB1100).
When I implemented the 'add cover img' option in Mobi2IMP 9.1, I thought that for the 'cover_nr.html' created, setting the top/bottom margins or padding for the <p> construct would help, but it doesn't. The bottom margin is simply ignored. The top margin needs something to "push-off' like a <div>‌</div>. The padding-top, padding-bottom don't effect the image shrinking performed internally by ETI's eBook Publisher. This is truly a 'bug' in eBook Publisher.
And a harder one to 'work-around' without ETI's help!