The new annotate feature is really spectacular :-). I find it so useful that I would like to use it to annotate not only the currently loaded image, but also images which I have saved previously. It is already possible to drag the currently shown image to the Desktop or Dolphin to move or copy it there or export it using the Export button. For me, it would feel natural to be able to drop an image file on the image area to import it. And/or have a button "Import image from... (file, clipboard)".
Spectacle already has this option in sort of a hidden fashion; see `spectacle -e`. But there's no need to use Spectacle for this; you can now edit in Gwenview using the same UI!