Then, a reflection is pulled in from the background image and a dropshadow is added.
Should be quite basic.
Probably another turbulence/dithering could have been added after the diffuse filter primitive, so then one of those could generate some texture and the other handle the low colour depth bending issue.
Also, another case where it was easier to use three flood fills then to generate shades upon the source image, which is always problematic.
Probably that worths more testing.