I see, I'll leave that decision up to you.

Back to this issue:
It would be nice if there was a possibility to generate the html code when inserting an image instead of the markdown syntax. That way, it would be easy to specify and change the width and/or height.

The methods to do this might already be implemented:
An image link written in markdown syntax is transformed into the html syntax when we the WYSIWYG editor to change its size.

Alternative idea:
A Joplin plugin that checks the notes markdown for the image resize syntax discussed above and replaces it with the proper html syntax before rendering the note. That way, the image resize syntax would just be a shortcut for writing the html syntax.

This regex substitution should do the trick:
regex:

/!\[(?<alt>.*)\]\((?<link>\S*) =(?<width>\d*)?(x(?<height>\d*))?\)/g

substitution:

<img src="$<link>" alt="$<alt>" width="$<width>" height="$<height>">

Original:

![Joplin logo](https://joplinapp.org/favicon.ico)
![Joplin logo](https://joplinapp.org/favicon.ico =400)
![Joplin logo](https://joplinapp.org/favicon.ico =200x400)
![Joplin logo](https://joplinapp.org/favicon.ico =x350)

Result

![Joplin logo](https://joplinapp.org/favicon.ico)
<img src="https://joplinapp.org/favicon.ico" alt="Joplin logo" width="400" height="">
<img src="https://joplinapp.org/favicon.ico" alt="Joplin logo" width="200" height="400">
<img src="https://joplinapp.org/favicon.ico" alt="Joplin logo" width="" height="350">

This way the markdown would stay portable but the user has the convenience of using the shortcut.

Sidenote: Apparently, setting the height via html is not supported in Joplin yet. I have created an separate issue for that: