Currently it's not possible to copy / cut and paste existing images in a document. This was confirmed by Jon from CU support.
Paste an image (e.g. Ctrl + v) into a document. Now you'd expect you can right click the image and copy / cut it or mark it and Ctrl+c / x it so it goes back into clipboard, but that's not available. While, if course, for texts it works as browser default.
So it would be great to also have this for images. The copy / cut should happen with the original sizes if the image or there should be an option to copy in original size or current size.
PS: Furthermore please check drag / drop / paste in tables, it doesn't seem to fully work as expected.