Pasting text without selection adds a new note with the clipboard text. This does not work for images on the clipboard if captured outside of Scapple. Copy an image in Scapple and pasting it in Scapple works fine.
Thanks, this bug has been fixed internally for the next update. Paste should work from just about any image source ideally. It was working from within Scapple, because within the program it uses its own private pasteboard which treats notes as special—this way you can copy and paste notes between boards and retain all of their properties, rather than just pasting them as raw text (or images as the case may be).