Gimp QuickStart for Mac OS X 10.11+
The Mac Tutorial Shows You Step-by-Step How-to Install and Getting-Started with The Gimp Program 2.8.16 on Mac OS X 10.11 El Capitan BSD.
GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring.
On Mac OS X 10.11 El Capitan The Gimp Installation via Homebrew is currently the most viable.

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Open a Shell Terminal emulator window
(Press “Enter” to Execute Commands) -
How-to Install Homebrew for Mac OS X:
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Installing The Gimp for Mac OS X 10.11 El Capitan
brew install gimp
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Launching Gimp
gimp