what type of images are they. Thunderbird can include jpg and some other formats. But all images are not created equal especially if they come in one of those Apple variants of real image formats.

Ensure that the menu item view > attachments inline is selected.

They are jpg files being sent from my LG phone running an Android OS.

The view attachments inline option has also been selected.

If it matters, this is Windows 7 Pro and Thunderbird is version 60.4.0 (32-bit).

I've also noticed that Bitdefender has added a toolbar, but this problem was occurring long before it was installed.

Mobile devices sometimes send email that is hard for TB to decode, e.g. non-clickable links. There are a number of explanations in this article:

http://kb.mozillazine.org/Images_in_messages_do_not_appear

After trying the simple steps, such as changing the View/Message Body as setting, open the message source (Ctrl+U) and look at the content-type header; if it's not image/jpeg, that may explain the problem, no matter whether the images are remotely-linked or not.

The address wasn’t understood

Firefox doesn’t know how to open this address, because one of the following protocols (cid) isn’t associated with any program or is not allowed in this context.

You might need to install other software to open this address.

This error was displayed when the message was saved, as suggested in the link above from sfhowes. All images and text messages appear normally on another computer using a different mail application. Whitelisting the phone number on my domain didn't fix it either.

open the message source (ctrl+U) locate the attachment in the message source.

It will have a form something like the following which comes from an email in my inbox.

Content-Type: image/png;
name="TB view more information about this update.png"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
filename="TB view more information about this update.png"

Please post that information from your email.

Content-ID:<Message_1546562724145> Content-Type:image/jpeg;Name="Message_1546562724145.jpg" Content-Location:Message_1546562724145.jpg Content-Transfer-Encoding:base64

Sorry, I forgot to include that in the previous response.

So there is no content-disposition: which is how email apps are supposed to determine if the attachment is for inline display or as an attachment. Which Thunderbird will normally display at the end of the.

Just to be sure my Guess here is not wrong could you forward the message to me as an attachment (click the down arrow beside the forward button) to matt_au@gmx.com

You're correct, others have similar issues when searching for a solution.

Any idea how to determine if it is the phone or the provider?

Which Android mail app are you using, and what happens if you send a message with an embedded image (not remotely linked)? Use the Insert/Image command on the phone, don't paste an image from the phone into the message body.

These are text messages being sent from my phone, with images taken using the camera application.

Images sent in the text message are not automatically displayed when viewed in Thunderbird, including the pieces of artwork that Tmobile adds. The image I attach, the dotted line, and the footer will appear in another application on the computer when double-clicked in Thunderbird's footer that shows the names of the files.

Since this isn't a Thunderbird issue, I may need to find an Android forum to see what can be done to send the messages differently.