It would be very helpful to be able to past a thumbnail from the clipboard rather than have to load it from a file.
For example, when looking at a file in the viewer, it would be useful to copy an image to the clipboard, then past the image back as a thumbnail.
Right now, on windows, this requires using a tool like the snipping tool to capture an image, then saving the image to a temporary directory, then opening windows explorer, opening the thumbnail change screen, then opening the file as a new thumbnail.