
Your HTML as it exists will not send the image with the email, it is also quite possibly not going to show it, instead offering the blocked images toolbar. Note the HTML tab in Thunderbird comes from this addon. Which the Thunderbird composer creates to look like This is what I generate in the Thunderbird composer.

That reason is fundamentally that the composer when used to save HTML will add appropriate tags for email, and where you have to include the image data in the email (where the file is local) then it will be incorporated into the HTML. There is a reason that we recommended composing the HTML in the Thunderbird composer, not some other product like dreamweaver.
:max_bytes(150000):strip_icc()/5SelectOpenannotated-f0b739a4bde241008e7a5ce8502f233e.jpg)
I have linked directly to the part of storage in a file because if you are using HTML with images there is little of any value you can do in the actual account settings HTML box.
