  Buchanan et al. [Nature 436, p. 475 (2005)] have shown that it is possible to
recognize paper samples via their speckle pattern by using a line-shaped laser
focus, four photo detectors and a scanning mechanism. In this report
recognition of five out of ten paper samples is presented. The sample was
illuminated by a 2.62 +- 0.02 mm circular spot and the reflected light was
measured by a static CCD. We have formulated a criterion for recognition that
limits the probability of false recognition to 0.1 % for the experiment with
ten samples. We obtained results that show that the probability of false
recognition will be negligible for a large amount of samples. The properties of
speckle originating from a line and a spot illumination source have been
compared to see whether the use of a line results in major advantages for the
recognition of samples.
