The screenshot on Gnome is not a default function. However we can install it and create our own shortcuts.
INSTALL
Use the following command to install screenshot on Gnome:
$sudo yum install gnome-screenshot
After that, we can use the function by the following command:
$gnome-screenshot -a //screenshot on Area
$gnome-screenshot -w //screenshot on window
…… //you can goto man pages to learn how to use it.
Also, we can create shortcuts on X-window.
Go System Preferences->Keyboard Shortcuts, and hit the button “Add”, it will pop up a dialog.
Fill out the name what you want, e.g.Area, and the command is gnome-screenshot -a, then click the button “Apply”. Then press the keys which will active the command to grab a area, and You will have done.