Taking Screenshots on Mac OS X

The keyboard shortcut for taking screenshots of a selected area on Mac OS X is: Cmd-Shift-4.  You may press space after the shortcut to capture a window.

1. To change the image format to PNG:
   defaults write com.apple.screencapture type png
2. To change disable the shadow in the screenshot:
   defaults write com.apple.screencapture disable-shadow -bool true
3. To take effect:
   killall SystemUIServer

More information can be found from Mac Guides.