a = Import["http://www.nefferport.com/21a/outputwhite.jpg"];
b = Import["http://www.nefferport.com/21a/outputcyan.jpg"];
c = Import["http://www.nefferport.com/21a/outputmagenta.jpg"];
d = Import["http://www.nefferport.com/21a/outputyellow.jpg"];
e = Import["http://www.nefferport.com/21a/outputblack.jpg"];
Manipulate[
 combine = r; 
 Which[r == 1, 
  Image[ColorCombine[{b, c, d, e}, "CMYK"], ImageSize -> 1000], 
  r == 2, Image[ColorCombine[{b, a, a, a}, "CMYK"], 
   ImageSize -> 1000], r == 3, 
  Image[ColorCombine[{a, c, a, a}, "CMYK"], ImageSize -> 1000], 
  r == 4, Image[ColorCombine[{a, a, d, a}, "CMYK"], 
   ImageSize -> 1000], r == 5, 
  Image[ColorCombine[{a, a, a, e}, "CMYK"], ImageSize -> 1000]]
 ,
 {{r, 1, "ink:"}, {1 -> "All (CMYK)", 2 -> "cyan (C)", 
   3 -> "magenta (M)", 4 -> "yellow (Y)", 5 -> "black (K)"}}]
Print["Note: These subliminal messages are not real; I made them up \
for the demonstration. Try looking for subliminal messages like these \
on the street."]
Print["Created by Ryan Neff, Harvard University, 1 December 2009. For \
private and educational use only (some of the images are subject to \
copyright of their respective parties."]