Markus Schönhaber:
Thunderbird generally can handle displaying images referenced via a cid URL. I often get mails containing images which are referenced this way and are displayed correctly. If you're viewing this post in HTML, you should see an image here (provided the list software hasn't stripped it) which is referenced via a cid URL:
Why this doesn't work in the provided sample mail, I don't know. Maybe (or maybe not) it's related to this: https://bugzilla.mozilla.org/show_bug.cgi?id=61815
jd1008:
Sorry to say that I find this totally unhelpful and it does not address the sample message I provided, which TB is unable to handle.
Did you read the bugzilla and look at the other message headers, to see whether the overall HTML message content-type headers in yours was like the bugzilla?
With a multipart message (text and pictures), there's one type of header you could expect. With a multipart alternative (a text version with a HTML version, there's another type. Some mail clients, particularly Microsoft ones, are infamous for creating outright broken message, so all bets are off regarding proper interpretation.
Here, using Evolution, I could see the disco dancing Fedora panda, and I noticed that its content ID was in the more usual form that looks somewhat like an email address (something@something), whereas the failing message had a simpler (RaNdOm) kind of ID. I don't know if that's an extra consideration, or not a problem at all.