My 10-year old grandson showed me this trick.
There is a little tool in most versions of Windows since XP called a “snipping tool” that can snip any part of the window you are viewing and save it as a jpg file. It is under “accessories” on my Vista machine.
Once you’ve saved it to your own machine, begin to write a new note, there is an “Attachment” button at the bottom of the editing screen on your note in expression engine. Click on that button then find the saved jpg file on your machine and upload it to your note.
Preview gives you an odd look at it, but it then seems to be OK when you post the note. Looks like you are permitted 3 attachment per note totaling 75 KB.
I don’t have a Mac, so this only relates to Windows.