I just pasted the image below from the Windows 7 snipping tool.
EDIT: Nope. It pastes into the dialog box and looks fine but it fails with the error "Message cannot exceed 20,000 characters.". If I then look at the HTML version, the image is a loooooong string of gibberish.
Looks like I was successful. But not without problems:
The first time I pressed "Post" I got the message
And after pressing "Post" again all seemed OK.
BTW I also tried to insert the screenshot above via paste from the clipboard but nothing happened when I pressed Ctrl-C. So I still had to save it and insert it the cumbersome way.