First, I do see the images, but not the cover on my reader: Mobipocket Reader v.5.3 - Build 582.
But:
I took the mobi file from your second post and parsed it through my scripts. I can see the images. (after getting the HTML using mobi2oeb)
I did have to make some changes, as I make sure my source files are epub compliant:
1. changed the order of the <guide> and <spine> in the .opf file
2. added the ncx file to the manifest in the .opf file
3. added the <?xml version?>, doctype and html xmlns to the HTML file
step 2 required me to make some minor changes to the file:
4. <font> isn't allowed, <a name> isn't allowed, <center> isn't allowed. I replaced those with a <span class="font-size">, <a id> and <div class="center">.
5. an image requires the "alt" attribute, so I added an alt="image" to all images
6. I had to add an extra <div> in the table of contents, as the <a> and <br/>'s aren't valid in a blockquote (apparently)
7. there are two loose <a> elements, I had to surround them in a <div> also.
My script makes an epub file from the sources, and then uses mobigen to create a mobi file.
The result does show all images and the cover.
----
The changes I made to the HTML file and the OPF file won't explain why they do show for me. But, the way I transform them does. I've no idea how to use Calibre to make mobi files, otherwise I'd use those sources and try to see what Calibre does...