OS X Screen Capture

To capture the screen on OS X :

⇧⌘4 : Selected area to capture.
⇧⌘4-space : Capture a window.

These are defined in the System Preferences.

To change the captured image from the Terminal (/Applications/Utilities/Terminal.app) type

Jpeg:

defaults write com.apple.screencapture type jpg
killall SystemUIServer

defaults write com.apple.screencapture type png
killall SystemUIServer

defaults write com.apple.screencapture type tiff
killall SystemUIServer

defaults write com.apple.screencapture type pdf
killall SystemUIServer