There could be several reasons why the image would remain relatively smaller than what you would expect, namely:
- perhaps the <img src="cover_image.jpg"> tag has the width= and height= specified to actually be smaller.
- perhaps the image reference in the <img src="cover_image.jpg"> is the wrong one; just rename it to the correct one by opening the exploded .html using a text editor and then rebuilding the .imp using the .opf with eBook Publisher.
- perhaps the .prc file didn't have the cover image flagged as a "cover" when using Mobipocket Creator and it was otherwise embedded in the .html as the first image and not necessarily a "cover".
If I was converting that .pdf ebook, I would have used a slightly different course of action, namely:
- Using the freely available Mobipocket Creator Publisher Edition v4.2 (Build 40 is preferred), Import the PDF ebook into Mobipocket Creator and have it convert that .pdf ebook to .prc directly. You may have to tweak the Metadata and Guide sections if you want a "better" .prc ebook.
- Using the latest Mobi2IMP enhancements** (you need to download the Mobi2IMP-9.4e.zip AFTER you use the Installer), convert that .prc ebook created above into .imp as per your previous conversion.
**I think you are still using the original Mobi2IMP (version 9.4) without any of the recent enhancements available since your dos window would have otherwise read
Mobi2IMP (version 9.4e) Copyright (C) 2009 Nick Rapallo (nrapallo) 