Change Screenshot Format in OSX

To change the default screenshot format in OSX:

Step One
Open a new Finder window and go to Applications : Utilities : Terminal


Step Two
Now you have to decide what format you would like to use as the default file format.

BMP (Windows bitmap), GIF, JPEG 2000 (what you chose), JPEG, PDF, PICT, PNG, PSD, SGI, TGA, TIFF

Step Three
Enter the following command into the Terminal window:
defaults write com.apple.screencapture type image_format

for example if you would like to change to png as default file format then enter this...
defaults write com.apple.screencapture type png


Step Four
The next time you take a screenshot it will be in the format you just set!