Since Kindle Previewer/KindleGen can handle ePubs, why don't you simply create an ePub in
Sigil and then convert it with Kindle Previewer?
Sigil will automatically put the Images in a separate folder, and if they're visible in Sigil's Book View mode, they'll also make it into the .mobi file.
Sigil will also automatically generate an .ncx file that is needed for chapter navigation. (This file cannot be generated with Mobipocket Creator.)