The max width 320px minus any margins in the HTML (we recommend using thumbnails to go to the full images) thumbnails should be 100-300px.
Images that are larger than the phone screen could be displayed as clickable thumbnails within an abstract to ensure a good phone reading experience. This is recommended for image sizes greater then 100kb. Ideally a small thumbnail image should be created at a much smaller file size for quicker loading (e.g. 10kb)
This can simply be achieved by setting the width of the image and linking to the source image directly and including this html when the abstract html is generated:
<a href="http://linktoimagefile…/image.png"><img src="http://linktoimagefile…/image.png" width="200px" /></a>