Is it possible to resize the images I drag and drop into the editor?
Not natively but there are a few things you can do.
Personally if I need a resized image I just use HTML instead of markdown i.e. rather than

I use:
<img src=":/5d2e97f37b2649b583d1cc03e987c6e7" width="400">
There is also a plugin (or plugins) that can do this such as the Attache plugin where it takes the source image and resizes it for you.
You can also change the size that images display using the plugin Joplin Enhancement
First, insert your image, and go to the markdown editor which will show, for example:

Now by adding, again for example, {width=50%}
, so it looks like this:
{width=50%}
the image will appear at half the original size (the image remains the same size it's just displayed according to what you've added in the curly braces)
Using a plugin for resizing images is definitely an amazing and effective solution.
Buidling upon the above answer, I use (though I can't remember where I found it and who to credit!):
<figure>
<img src=":/272198a227744a058467bd1c66140daf" width="500" height="100">
<figcaption> Fig. 1: My figure caption. </figcaption>
</figure>
I can never remember the syntax though so I save it in another note.
The only thing I'd like is to make the caption text italicised, but it doesn't accept the markdown syntax for that
If you add the below to userstyle.css and quit and restart Joplin all your <figcaption>
s will be italic.
figcaption {
font-style: italic;
}
More info on the <figure> tag can be found here.
Thank you, that's great! I'd never used the userstyle.css before, but now see lots of people tinker with it, now I have started too!