How does pasting an image work, e.g. when composing a PF post?

[Swamp Thing]

TL;DR

How to implement this thing where you can paste an image when composing a post on Physics Forums?

I have pasted the image below after copying it from my desktop. The image becomes visible in the Post Composer as soon as you paste it. It also works if you copy from another web page.

I assume that JavaScript is able to grab the data from the clipboard and create an IMG element on the fly, and also send the IMG data to the PF server. It can also create a thumbnail version.
How to code these functions?

 

[jedishrfu]

Perhaps @Greg Bernhardt can answer this best.

 

[Greg Bernhardt]

The editor is Froala
https://www.froala.com/wysiwyg-editor

 

[Swamp Thing]

Thanks!