A GIMP image may be quite a complicated thing. Instead of thinking of it as a sheet of paper with a picture on it, think of it as more like a stack of sheets, called “layers”. In addition to a stack of layers, a GIMP image may contain a selection mask, a set of channels, and a set of paths. In fact, GIMP provides a mechanism for attaching arbitrary pieces of data, called “parasites”, to an image.