If you have an image saved to your system clipboard, it's possible to paste this directly into a WYSIWYG editor (either Atto or TinyMCE) using Firefox or Internet Explorer (latest, and presumably previous versions at time of writing).

However, this no longer works in Chrome.

And yet, Chrome can still paste images from the clipboard, which easily be tested by writing an email in gmail for example, so not an issue with Chrome per se it seems.

As far as we're aware, it was working roughly 6-9 months ago, and doesn't seem to be affected by moodle version (certainly 3.3.1+, 3.1.3+).