When you import an image as an ArtRage painting, ArtRage adds 'depth' to the paint. It makes the paint thick, like the thick oils. When you import an image as a layer it doesn't add any depth to the paint. The paint is thin, like airbrushed paint.
Note that if you import a PNG or PSD with any transparency, no thickness will be added. Making the paint thick where there are transparent edges gives visible ridges, which you probably dont want.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"