The only difference I have seen any mention of between an AZW and a MOBI file is a single integer. This is the case for DRMed files, see Aenea's post
. I don't know if DRM-free AZW even has the extra integer, but in any case (as delphidb96 said) DRM-free AZW and MOBI are interchangeable.
For images in MOBI files, see Images in MobiPocket