I asked this question, but the images I used are rather large. Can you/how can you resize images in the question (short of downloading the image, resizing it on the computer, and re-uploading the question)?
This feature exists, it's documented in the advanced help.
You can also use standard HTML image syntax, which allows you to scale the width and height of the image.
<img src="https://example.com/sample.png" width="100" height="100">
There's also a quick way of resizing images that have been uploaded to Stack Exchange's servers (or any imgur server, in fact). From Resizing an image in a post?: given an image URL like
l before the
https://i.stack.imgur.com/admM6s.jpg, etc.) to scale down the image to a predefined size.