The "View All Body Parts" add-on may help you but I'm having trouble finding suitable Junk to test it on.

Of course, one reason for masking images in suspicious email is that the action of viewing them can trigger a download from a webserver, which serves to register yours as a working valid email address.

There is a very good reason why you should not auto allow remote content. Please read so you understand the risks. http://kb.mozillazine.org/Privacy_basics_(Thunderbird)

Thank you for your reply. I most certainly do not wish to Auto Allow remote content, for the very good reasons you suggest. What I want to do is have an Options box on junk mail, like the one in the In Box, where I can selectively view remote content for a specific email where I trust the sender, so that I can quickly view the graphics on commercial offers etc that I may be interested in.

If you trust the sender, un-junk it. Messages from a known and trusted sender cannot be "unsolicited commercial email", surely?

I only allow emails into my In Box from addresses in my address book. 95% plus of items, some 40 or so items per day, go into Junk. I scan them, look at items that may be of interest, then Ctrl/A to select the lot and Delete. I find this the most efficient way to deal with emails.

Edward01 said

I only allow emails into my In Box from addresses in my address book. 95% plus of items, some 40 or so items per day, go into Junk. I scan them, look at items that may be of interest, then Ctrl/A to select the lot and Delete. I find this the most efficient way to deal with emails.

I suggest you move mail from those in your address book into a folder other than the inbox perhaps call in known senders. Leave the other stuff in your inbox as it is not junk, just mail from unknown senders. A simple change that will get you what you want

Matt, many thanks for your, most helpful, suggestion. If I cannot find a way to display Remote Content in Junk, as I have with other email programs, then I will certainly look at this one.