The next release will fix numerous copy and paste problems in general, some of which are reported in our Trouble Reports section. There is another related forum post with an answer provided by Titan which you will all find interesting: https://www.nomachine.com/forums/forums/topic/selection-using-mouse-disappears#post-2153
@drichards, copy and paste of images isn’t possible, rather in the future it will be possible to drag and drop them. The current mechanisms for copying images between server and client (version 4.x) are file-transfer and disk sharing.