Great info, thank you for your help.
have assumed that GIF and JPEG is OK. In my html2mobi and lit2mobi programs I convert everything to JPEG. There is a maximum size for the image (64K I think).
I want to show the current artwork, the Cybook would show. So getting the image with offset n can only work if I identify all image resources. Well. For now I just assume there is only gif, png and jpeg, until proven wrong.
Now only my Cybook needs to arrive, so I can see if all works well.