<i>The method requires access to sophisticated equipment that can create very tiny features, roughly 500 times smaller than the width of a human hair</i><p>Semiconductor fabs are doing this already, in the form of MEMS devices. The setup cost is not cheap, but not all that expensive either for determined counterfeiters.<p>This reminds me of holograms and microprinting - they were (and still are) considered great anti-counterfeiting measures, but now you can buy sheets of them printed with whatever you want for next to nothing. If this technology becomes popular, it might not be long before these "hidden images" end up everywhere.<p>If there was an easy way to test the <i>drug itself</i> for the right quantity and composition, I think that would be a much better solution, although somewhat more difficult in practice... for some reason this reminds me of <a href="http://xkcd.com/810/" rel="nofollow">http://xkcd.com/810/</a>