what is the format of the image?
and are the images being defined in <img></img> tags or <svg><image></image></svg>?
The kindle won't do the latter, and some conversion tools utilize it (tis valid afterall, I believe)
also check that all the images are being properly defined in the OPF.
As to your navigation, I believe kindle will take chapter order from spine in the OPF (don't quote me on that), and builds it's table of contents from the Table of contents page defined in the guide in the OPF. So your chapters should probably be in different files. (not just one big long one!)
Also it might be worth checking your epub with epubcheck (or flightcrew), and making sure that your kindlegen isn't producing any errors.
If your still having issues feel free to send us an email at
mail@stunjelly.com, and we might be able to help you further!