Copy of an image from Gwenview to the clipboard, it does not work.
For example, i want to copy an image from Gwenview into Gimp without loading images-file.

gThumb works, but it is GTK, not Qt.

We are currently working on that feature in https://phabricator.kde.org/D12871, most likely it will be available starting with Gwenview 18.08.

As a workaround until then, you should be able to drag the image from either Browse mode or the Thumbnailbar onto GIMP.

Thank you!