Mac OS X Specifics
As of Mac OS X v10.4, Preview now has a Grab submenu in the File menu, with selection, window and timed screen.
Similar the Mac Mail app has Grab built-in - users right click the mouse while typing email, to add a screen capture.
In Mac OS X, it is also possible to save screenshots directly to the Desktop in .pdf format (earlier versions of OS X) or PNG format (later versions), using keystrokes shown below. It is not possible to use this software while DVD Player is open.
Grab helps determine the size of an element on the screen. By using the selection feature and capturing the screen, one can go to "Edit" > "Inspector" from the menu or press Cmd+1; a dialog box will appear with the dimensions of the selected area.
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Screenshot of Inspector feature
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