Adding an image to email invite

When customizing the template for forum invite emails, I cannot see how to embed a small image at or near the top (in this case a logo).

How should this best be done?

Dragging and dropping seems to work (with limited control over resulting image size) when composing normal posts, but not in the template editor.

I found I could place an image using markdown and a link to an externally hosted image - but this implementation of markdown does not seem to allow control over image size at all - as a result the forum logo appears at full width of the email message, scaling up and down to suit message window.

Using html seems to offer better control over sizing in emails - eg

<img src="" alt="NZ architecture Forums" width="200"/>

But weirdly enough the same approach does not seem to work with a normal forum post - only a place holder for image appears at first, even as an email from same will show the image - and the posted version seems to ignore the sizing (when it does appear) even as the email version seems to respect it.

There also seem to be stubborn problems with caching of the image every time you want to update it with this approach, that don’t seem to apply with the direct drag and drop approach. Clearing browser cache alone does not seem to suffice.