Traditionally, Orton photography was a darkroom technique that involved a sandwich of two exposures of the same scene, generally with one out of focus. This resulting images would be soft and surreal with slightly unnatural lighting.
Fortunately, it is very easy to recreate this style of photography in the digital age using GIMP. The digital technique is very closely aligned to the darkroom process in that more than one image of the same scene are 'sandwiched' using the Layers palette.
By following this tutorial, you'll be introduced to using the Layers palette as well as taking advantage of its different Layer Modes and opacity control. You can use any image for this tutorial, but please feel free to download this copy of the image that I've used: IP_bike_2000.jpg