Shortcuts for taking pictures of the screen
In addition to the Grab application, you can also use keyboard shortcuts to take pictures of the screen in Mac OS X.
To take a picture of the whole screen, press Command-Shift-3.
To take a picture of part of the screen, press Command-Shift-4 and drag to select the area you want.
The picture is saved as a TIFF file on your Desktop. Note: Mac OS X 10.2 and later saves pictures as PDF files. See document 107078 “Mac OS X 10.2: Screen Shots Are Saved in PDF, May Be Converted” for additional information.
To copy the screen capture to the Clipboard instead of saving it as a file, press Control-Command-Shift-3 to copy the entire screen to the Clipboard, or Control-Command-Shift-4 to copy the selected range to the Clipboard.