How to copy part of an image using Apple Pencil
Here's what I did.

With the Google search result image you want to use on screen, swipe diagonally up from the bottom left corner of the iPad screen. This will take a screenshot.
You have to use your fingers for this bit, but crop your screenshot to just the part of the image you want to copy.
In the top right corner use the share icon (arrow pointing up from a square).
Select &quot;Copy&quot;
Switch to OneNote
Paste!

You can also add OneNote to the share menu to share directly. In this little video I've already added it to mine.
https://imgur.com/a/RDKzUJC