Use Terminal:
Change the screenshot format to JPG
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type jpg;killall SystemUIServer
Change the screenshot format to GIF
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type gif;killall SystemUIServer
Change the screenshot format to PDF
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type PDF;killall SystemUIServer
Change the screenshot format to PNG
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type png;killall SystemUIServer
Change the screenshot format to TIFF
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type tiff;killall SystemUIServer
Change the screenshot format to JPG
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type jpg;killall SystemUIServer
Change the screenshot format to GIF
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type gif;killall SystemUIServer
Change the screenshot format to PDF
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type PDF;killall SystemUIServer
Change the screenshot format to PNG
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type png;killall SystemUIServer
Change the screenshot format to TIFF
Type or paste the following line into a Terminal window and hit the Return key to execute the command:
defaults write com.apple.screencapture type tiff;killall SystemUIServer