My Operating system is Lubuntu 14.04 (currently). The default screenshot application is called scrot. When you use the keyboard shortcut, scrot silently deposits the screenshot image in ~/home. Unfortunately, it does not put a copy in the clipboard.
For the Dokuwiki imagepaste plugin to work, the image must be in the clipboard.
I installed gnome screenshot using the package manager, when you take a screenshot with gnome-screenshot, you get the option to copy to clipboard.
After installation, screenshot appears in the menu under Accessories.
Dokuwiki imagepaste plugin only works with the chrome browser, see the installation page:-
Save screenshot to clipboard, then CTRL+V to paste into a dokuwiki page opened for editing.