Life-related signal detected from a finger-tip can be used to prevent frauds by finger-replicas. A finger deformation induces blood movement and the light scattered inside the finger carries this life-related information. We propose to look at the changes in color and luminance extracted from the central part of the fingerprint images. In experiments, we examined input actions taken by more than 30 participants as well as six replicas made of various materials. For
the live fingers, chromaticity coordinates x and luminance Y showed a relatively large hysteresis as a function of the area of the fingerprint images. This hysteresis was smaller in case of the replicas. Based on this fact, we were able to define indices and criteria for life recognition so that all the replicas were rejected while the most live fingers were accepted. However, the recognition was not perfect due to the small hysteresis shown by some replicas.
Improvements in the input hardware and the algorithms for life-related information extraction need to be addressed in future.
Counterfeiting a finger will become an important issue for unattended fingerprint identification. To fight against this threat, we have proposed to look at the color changes in a deformed finger during an input action. When a finger is pressed upon an optical fingerprint sensor, it is gradually deformed and the color of the fingerprint images changes. This is due to the blood movements inside the finger. If the extent of this color change exceeds a certain threshold, we judge that the finger is alive. In this paper, we report on the spectral changes of the light scattered by a deformed finger first. As the pressure applied to the finger increases, the relative intensity of the red portion of the spectrum decreases. Even after the pressure is off, it takes some time for this intensity to recover to its original value. Second, we discuss a dual-LED imaging system based on scattered light detection. Here, red and green-emitting LEDs are mounted on an edge of a plastic plate which serves as a light-guide. The light scattered by a finger placed on this light-guide is captured by a standard color camera. Based on the experiments conducted on several types of replicas as well as 42 volunteers, we show that this system is capable of identifying the live fingers. Signal extraction process is investigated for stable separation between live fingers and replicas. A model based on the blood movement inside a finger is developed. A mobility-index is proposed and is correlated with the ages of the volunteers participated in this study.