Update 2010-12-06: Ray points out that you can do this with gconf-editor, which is a much better solution.
It’s a handy feature of Gnome that pressing “PrntScrn” or “Alt+PrntScrn” will take a screen capture of the desktop or current window, respectively. However, in typical Gnome fashion, you can’t do anything more advanced. You can’t capture a region, or a window area. You can’t delay the capture. You can’t save the captures with iterating, numbered filenames. However, the equivalent KDE tool can do all of those things, and you can make Gnome use it.
When you press the PrntScrn key, Gnome calls
gnome-screenshot. When you press Alt+PrntScrn, it calls
gnome-screenshot --window. Again, typical Gnome design means you cannot configure what command is called. But you can make your own
gnome-screenshot script which calls
Create a script in /usr/local/bin or $HOME/bin (if you have that in your path), and edit it.
sudo touch /usr/local/bin/gnome-screenshot
sudo chmod 755 /usr/local/bin/gnome-screenshot
sudo vi /usr/local/bin/gnome-screenshot
Now paste in the following:
#!/bin/sh if [ "$1" = "--window" ] ; then ksnapshot -c else ksnapshot fi
Save and quit, and you’re done! Pressing PrntScrn now opens