These runtime libraries need to be downloaded and installed in order to run the main program, The Gimp. Install GTK+ Runtime Environment before installing The Gimp.
GIMP (GNU Image Manipulation Program) is a freely distributed piece of
software suitable for such tasks as photo retouching, image composition
and image authoring. It is a powerful piece of software with
capabilities not found in any other free software product. 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, and an image format converter.