Barcodes have become ubiquitous. Many industrial goods and supplies include them to support supply-chain management and allow routing. Most consumer products sold in retail stores contain barcodes used for automated checkout, inventory control, and other functions. They appear on tickets to concerts, sports events, and other high-value venues. Pharmaceutical packaging often incorporates one or more barcodes. But each of these application areas is plagued with the problem of counterfeits. Incorporating a copy-resistant feature would deter attempts at counterfeiting.
A number of attempts have been made to produce copy-resistant barcodes based on specialized inks that can be checked for authenticity. Such inks may contain exotic particles such as quantum dots1 or have chemical, spectral, or environmental qualities that may limit applications for which they are suited. An alternative approach relies on a special high-resolution pattern that is printed in close proximity to a barcode,2 which reportedly cannot be copied by conventional means without producing image artifacts. Apart from the specialized printing process required, a drawback of this approach is that the security feature is separate from the barcode, thus increasing vulnerability. To address these shortcomings, we have developed a method of producing barcodes that have integrated security features and can be fabricated using readily available materials and processes.
Our method uses standard holographic material that is already in common use for security labels. We also use a standard printing process, such as heat transfer, to print an opaque barcode directly on the holographic substrate (see Figure 1). The barcode can be read and authenticated using a multi-imaging system, in which a series of images are rapidly collected under illumination from multiple directions using a configuration like that in Figure 1. The resulting set of images is then processed to extract a usable barcode image and authenticate its holographic features and any other security features that may be present.
Figure 1. Multi-imaging system used to acquire images of a barcode. The system is comprised of a digital imager and six different illumination LEDs. Each LED is illuminated individually, resulting in six different images. Inset: Example of a copy-resistant barcode fabricated by printing an opaque barcode on a holographic substrate.
When a copy-resistant barcode is imaged by such a multi-imaging system, the amount of light returned from holographic elements will vary considerably under different illumination angles, while the light returned by the nonholographic features will remain fairly constant. Figure 2 shows six images of a copy-resistant barcode acquired under six different illumination states (see Figure 1). A barcode image suitable for subsequent decoding may be readily generated from this sequence of images by performing a minimum operation on the six values for each pixel. Figure 3 shows the results for a genuine copy-resistant barcode and a nonholographic color copy. The genuine barcode has high contrast and can be decoded using common software, while the copy exhibits severe artifacts that limit decoding operations.
Sequence of raw images collected under the six different illumination states of the multi-imaging system in Figure 1
Figure 3. Pixel-wise minimum operation applied to sequences of six images acquired from (left) a genuine barcode and (right) a nonholographic copy.
The barcode's authenticity may be confirmed using a variety of methods, the simplest of which ensures that the holographic regions of the barcode vary significantly across the multiple illumination conditions. The range of the six values (i.e., maximum–minimum) for each pixel is one way to quantify this variation. Figure 4 shows range images for both a genuine barcode and a copy. The copy demonstrates much less range over the six illumination states than the genuine barcode. This can be used as a basis to reject nonholographic copies.
Figure 4. Pixel-wise range calculated from sequences of six images acquired from (left) a genuine barcode and (right) a nonholographic copy.
We expect that the availability of a viable technology for producing copy-resistant barcodes will decrease the incidence of counterfeiting and product piracy. Therefore, we have developed this technology based on standard materials and processes used in many manufacturing environments. We are currently developing additional security features that may be used to authenticate a genuine barcode. We are also seeking business partnerships to commercialize the technology.
Robert K. Rowe
Robert Rowe co-founded Lumidigm in 2001 and is its chief technology officer. He has over 20 years of experience developing sophisticated optical systems for imaging and measurement. Robert Rowe has a PhD in optics and is listed as an inventor on more than 100 granted and pending patents.