Norimitsu Akiba

Fluorescence spectra and images of latent fingerprints excited with a tunable laser in the ultraviolet region.

Fluorescence spectra of sebum‐rich latent fingerprints were studied with a tunable laser for non‐destructive fingerprint detection without chemical treatment. The tunable laser consists of a nanosecond pulsed Nd‐YAG laser and an optical parametric oscillator (OPO) crystal. The fluorescence spectra and images were measured at various excitation wavelengths in the ultraviolet region by the time‐resolved fluorescence method. We have previously reported that a typical fluorescence spectrum of fingerprints consists of two peaks located at c. 330 and 440 nm. In order to determine the wavelength of optimal excitation, excitation spectra were measured at wavelengths ranging from 220 to 310 nm. The fluorescence intensity of the 330 nm peak became maximal with excitation at 280 nm. The images of latent fingerprints on white papers were also measured and the clearest image was obtained with excitation at 280 nm. The influence of continuous irradiation on the fluorescence of fingerprints was measured at the optimal excitation wavelengths. The 330 nm peak was strong at first and decreased with continuous irradiation, whereas the 440 nm peak, which was weak at first, increased gradually.

Ultraviolet Fluorescence Spectra of Fingerprints

We have studied inherent fluorescence spectra and imaging of fingerprints in the deep ultraviolet (UV) region with a nanosecond-pulsed Nd-YAG laser system that consists of a tunable laser, a cooled CCD camera, and a grating spectrometer. In this paper, we have studied UV fluorescence spectra of fingerprints under 266-nm illumination. Fluorescence spectra of fingerprints have two main peaks, around 330 nm (peak A) and 440 nm (peak B). At first, when a fingerprint has just been pressed, peak A is dominant. However, its intensity reduces as the total illumination time increases. On the other hand, peak B is weak at first. It appears after enough 266-nm illumination and its intensity increases as time elapses. After 3 h of illumination, peak A almost diminishes and peak B becomes dominant. By leaving the fingerprint under a fluorescent lamp in a room without laser illumination, peak A can be restored partly, while the intensity of peak B still increases.Time-resolved fluorescence spectra were also measured for these two peaks. The lifetime of each peak is 2.0 nsec (peak A) and 6.2 nsec (peak B) on average. Both peaks seem to consist of several components with different lifetimes. In the case of peak A, the 330-nm peak decays fast and a new component at 360 nm becomes dominant when the delay time exceeds 20 nsec. In the case of peak B, unlike peak A, no clear peak separation is observed, but the peak position seems to move from 440 to 460 nm when the delay time becomes larger.

Visualizing Latent Fingerprints on Color-Printed Papers Using Ultraviolet Fluorescence

Abstract:  Laser detection of latent fingerprints on a white paper has been performed, previously. Ultraviolet fluorescence from various kinds of printer toner and ink used for home printers were measured to study fluorescence imaging of fingerprints on a color‐printed white paper. The experimental system consisted of a nanosecond pulsed tunable laser and a cooled CCD camera. Excitation wavelengths are 230 and 280 nm. Fourteen printers consisting of three color laser printers, three color inkjet printers, five monochrome laser printers, two monochrome copy machines, and a color copy machine were tested. Toner and ink of most printers exhibited fluorescence in the region from 360 to 550 nm. In most cases, clear fluorescence images were obtained by time‐resolved imaging with a band‐pass filter and 280‐nm excitation. However for toners from laser color printers that showed strong fluorescence, better results were obtained with 230‐nm excitation. Latent fingerprints on a photograph page and a black‐character page of a newspaper were also imaged.

Ultraviolet Fluorescence Imaging of Fingerprints

We studied fluorescence imaging of fingerprints on a high-grade white paper in the deep ultraviolet (UV) region with a nanosecond-pulsed Nd-YAG laser system that consists of a tunable laser and a cooled CCD camera.Clear fluorescence images were obtained by time-resolved imaging with a 255- to 425-nm band-pass filter, which cuts off strong fluorescence of papers. Although fluorescence can be imaged with any excitation wavelength between 220 and 290 nm, 230 and 280 nm are the best in terms of image quality. However, the damage due to laser illumination was smaller for 266-nm excitation than 230- or 280-nm excitation.Absorption images of latent fingerprints on a high-grade white paper are also obtained with our imaging system using 215- to 280-nm laser light. Shorter wavelengths produce better images and the best image was obtained with 215 nm. Absorption images are also degraded slightly by laser illumination, but their damage is smaller than that of fluorescence images.

CCD fingerprint method for digital still cameras

We have reported the Charge Coupled Device (CCD) fingerprint method for identification of digital still cameras. The CCD fingerprint method utilizes the nonhomogeneous nature of dark currents in CCDs. In this study, we have measured CCD defects patterns of various digital still cameras including professional cameras and cheap ones with various resolution and compression rates. As a result, CCD defect pattern was detected in all cameras except for a low-resolution cheap camera using only one image. Resolution mode change of digital cameras did not affect the position of defect points in general but in some cases, relative pixel intensity varied. Image compression did not affect the pixel position for blank images within normal compression rate, but when there existed light in the background, the pixel position was blurred as the compression rate became high. In conclusion, it is recognized that the CCD fingerprint method can be applied in principle to digital still cameras, that is, individual camera identification can be achieved in principle by using images taken with the camera.

Case studies and further improvements on source camera identification

Actual case examples and further improvements on source camera identification are shown. There are three specific topics in this paper: (a) In order to improve performance of source camera identification, the hybrid identification scheme using both dark current non-uniformity (DCNU) and photo-response non-uniformity (PRNU) is proposed. The experimental results indicated that identification performance would be improved by properly taking advantage of their features; (b) Source camera identification using non-uniform nature of the CCD charge transfer circuit is proposed. The experimental results with twenty CCD modules of the same model showed that individual camera identification for dark images was possible by the proposed method. Furthermore, it was shown that the proposed method had higher discrimination capability than the method using pixel non-uniformity when the number of recorded image was small; (c) The authors have been performed source camera identification in the five actual criminal cases, such as homicide case, and so on. The analytical procedure was a sequential examination of hot pixel coordinates validation followed by the similarity evaluation of sensor noise pattern. The authors could clearly prove that the questioned criminal scenes had been recorded by the questioned cameras in four cases of the five.

Individual Camera Identification Using Correlation of Fixed Pattern Noise in Image Sensors

Abstract:  This paper presents results of experiments related to individual video camera identification using a correlation coefficient of fixed pattern noise (FPN) in image sensors. Five color charge‐coupled device (CCD) modules of the same brand were examined. Images were captured using a 12‐bit monochrome video capture board and stored in a personal computer. For each module, 100 frames were captured. They were integrated to obtain FPN. The results show that a specific CCD module was distinguished among the five modules by analyzing the normalized correlation coefficient. The temporal change of the correlation coefficient during several days had only a negligible effect on identifying the modules. Furthermore, a positive relation was found between the correlation coefficient of the same modules and the number of frames that were used for image integration. Consequently, precise individual camera identification is enhanced by acquisition of as many frames as possible.

Visualization of Aged Fingerprints with an Ultraviolet Laser

Detection of aged fingerprints is difficult because they can degrade over time with exposure to light, moisture, and temperature. In this study, aging fingerprints were visualized by time‐resolved spectroscopy with an ultraviolet‐pulsed laser. Fingerprints were prepared on glass slides and paper and then stored under three lighting conditions and two humidity conditions for up to a year. The fluorescence intensities of the fingerprints decreased with time. Samples were stored in the dark degraded less than in sunlight or under a fluorescent lamp. Samples were stored under low humidity degraded less than under moderate humidity. As the storage period increased, a fluorescence emission peak appeared that was at a longer wavelength than the peak visible in earlier spectra. This peak was used for visualization of an aged fingerprint over time. An image of the fingerprint was not initially visible, but an image appeared as the time since deposition of the fingerprint increased.

Wide-field time-resolved luminescence imaging and spectroscopy to decipher obliterated documents in forensic science

Abstract. We applied a wide-field time-resolved luminescence (TRL) method with a pulsed laser and a gated intensified charge coupled device (ICCD) for deciphering obliterated documents for use in forensic science. The TRL method can nondestructively measure the dynamics of luminescence, including fluorescence and phosphorescence lifetimes, which prove to be useful parameters for image detection. First, we measured the TRL spectra of four brands of black porous-tip pen inks on paper to estimate their luminescence lifetimes. Next, we acquired the TRL images of 12 obliterated documents at various delay times and gate times of the ICCD. The obliterated contents were revealed in the TRL images because of the difference in the luminescence lifetimes of the inks. This method requires no pretreatment, is nondestructive, and has the advantage of wide-field imaging, which makes it is easy to control the gate timing. This demonstration proves that TRL imaging and spectroscopy are powerful tools for forensic document examination.

Differentiation of black writing ink on paper using luminescence lifetime by time-resolved luminescence spectroscopy

The time-resolved luminescence spectra and the lifetimes of eighteen black writing inks were measured to differentiate pen ink on altered documents. The spectra and lifetimes depended on the samples. About half of the samples only exhibited short-lived luminescence components on the nanosecond time scale. On the other hand, the other samples exhibited short- and long-lived components on the microsecond time scale. The samples could be classified into fifteen groups based on the luminescence spectra and dynamics. Therefore, luminescence lifetime can be used for the differentiation of writing inks, and luminescence lifetime imaging can be applied for the examination of altered documents.