The GIMP (GNU Image Manipulation Program) is a freely distributed program for such tasks as photo retouching, image composition and image authoring. It has many capabilities. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc.
Installation Note: GIMP has issues when running from a location with non-ANSI characters in the path.
Upgrade Note: GIMP Portable 2.10.0 Rev 2 and later will archive your existing plugins from version 2.10.0 and earlier within the GIMPPortable\Data\plug-ins-pre-2.10 directory to eliminate issues with incompatible plugins due to a new major version of GIMP. You can manually copy your plugins back to test compatibility.
Unofficial Patch: The official GIMP 32-bit build for 2.10.x releases is broken and will not allow opening or saving files. GIMP Portable has a patch to downgrade GLIB to a version that correctly works.