[VM] VM displaying images

[jrd]

Hi folks.  Apologies ahead of time if this is a dumb question; I
researched a bit and didn't find anything which looks apropos.

I have a situation where VM sometimes displays inline images, and
sometimes doesn't, and it's not obvious to me why.  Is there a good
way to enable debugging of message display processing, so I can get a
handle on the decisions which are being made?  Alternatively,
suggestions on where I could start instrumenting the code to dig into
it?  I'm reasonably fluent in el, just looking for hints on where to
poke.

I'm running gentoo x86-64
kernel 3.2.2
emacs 23.4
vm 8.1.2
w3m 0.5.3

Thanks in advance...