Images in Thread Replies

I've seen people post images in thread replies but I can't figure out how to do it myself. Is there some trick I'm missing or was it a feature that's been removed?

It's still a thing! Basically what you need is a link to whatever image you're trying to share.
(when I try to share an image I created, I usually upload it into one of my galleries and copy that url).
Usually it's immediately displayed as an image like so:

(the actual url looks something like this: 'https://notebook-content-uploads.s3.amazonaws.com/content/uploads/original/ec6a5797-cd13-423d-958c-757f2285d86c.jpeg?1533652484')

The safest bet when you have questions on how this website works is stalking this thread by the ever-spectacular all-knowing @Riorlyne.