We have ideas that minutiae information is personal and sufficient to identify an individual, and interoperable among different databases, this question becomes less important. However, since many proponents of biometric systems make a claim that a fingerprint image cannot be reconstructed from a minutiae template, we will address this issue.
Until recently, the view of non-reconstruction was dominant in the biometrics community. However, over the last few years, several scientific works were published that showed that a fingerprint can, in fact, be reconstructed from a minutiae template. The most advanced work was published in 2007 by Cappelli. The authors analyzed templates compatible with the ISO/IEC 19794-2 minutiae standard. In one test, they used basic minutiae information only (i.e. positions x, positions y, and directions). In another test, they also used optional information: minutiae types, Core and Delta data, and proprietary data (the ridge orientation field in this case). In all the tests, the authors were able to reconstruct a fingerprint image from the minutiae template. Very often, the reconstructed image had a striking resemblance with the original image. Even though this reconstruction was only approximate, the reconstructed image was sufficient to obtain a positive match in more than 90% of cases for most minutiae matchers.
The potential repercussions of this work for the security and privacy of fingerprint minutiae systems are as follows:
- The fingerprint image reconstructed from the minutiae template, known as a “masquerade” image since it is not an exact copy of the original image, will likely fool the system if it is submitted.
- A masquerade image can be submitted to the system by injecting it in a digital form after the fingerprint sensor.
- A malicious agent could also create a fake fingerprint and physically submit it to the sensor. The techniques of creating a fake fingerprint are inexpensive and well-known from the literature.
- The ability to create a masquerade image will increase the level of interoperability for the minutiae template. The masquerade image can be submitted to any other fingerprint system that requires an image (rather than a minutiae template) as an input. No format conversion of the minutiae template would be required. Moreover, the minutiae template can be made compatible even with a non-minutiae fingerprint system (these systems are rare, however).