Ubuntu uses gnome-screenshot as the default screen grab tool. It calls gnome-screenshot to take a screen capture of whole screen or current window when pressing “PrntScrn” or “Alt+PrntScrn” key.
This tutorial shows how to replace gnome-screenshot, make your Ubuntu calls ksnapshot or shutter or whatever screen capture tool you like to take screenshots when you pressing down “PrntScrn”.
gconf-editor via Software Center, or this command:
sudo apt-get install gconf-editor
Then launch it (configuration editor) and navigate to “apps >> metacity >> keybinding_commands”, change the value of ‘command_screenshot’ and ‘command_window_screenshot’.
Now, PrntScrn calls ksnapshot.