Textures ID paper and plastic

Researchers from Imperial College London, Durham University and the University of Sheffield in England have developed a way of uniquely identifying documents, credit cards and product packaging.

The method involves scanning using ordinary laser scanners to produce unique identification numbers based on the microscopic textures of the objects' surfaces. An object is authenticated by scanning it and comparing the results to a scan made at the time the object was manufactured.

The method hinges on the ability of lasers to record the patterns of microscopic surface features and on the lack of any known method of reproducing or altering those features.

The probability of any two pieces of paper sharing the same surface fingerprint is 10^-72, according to the researchers. This is less than one in the estimated number of atoms in the universe. For smoother surfaces like plastic and coated paperboard the probability is 10^-20, which is less than one in 100 billion billion.

The researchers' prototype scanner shoots a laser beam across a surface and records the intensity of the reflected light via four photodetectors. As the lightwaves bounce off the microscopic hills and valleys of the surface, they interfere with each other to increase and decrease the light's intensity. The fluctuations in intensity above and below the mean value are converted into the 1s and 0s of a digital code.

The challenge to making the system practical was tuning the system to record the intrinsic microscopic irregularities while ignoring creases, dirt and other alterations, according to the researchers.

The researchers tested the method by scanning a piece of paper to get the initial measurement, then wadding it up, soaking it in water, scorching it, scribbling on it with ballpoint pen and marker, and scrubbing it with an abrasive cleaning pad. Despite the abuse, they were able to identify the paper using the method.

The method can be used now, and the researchers have launched a startup company to commercialize the technology. The work appeared in the July 28, 2005 issue of Nature ('Fingerprinting' documents and packaging).