# Realization of Impression Evidence with Reverse Engineering and Additive Manufacturing
## 3 Results
### 3D Reconstruction of 2D Latent and Visible Impressions  
2D photography has always been the most important tool for documentation and analysis of forensic 2D latent and visible impressions. However, transforming 2D forensic images into 3D digital and 3D printed physical reconstructions is a new approach to forensic data representation. A 3D digital reconstruction based on 2D photo can markedly enhance the available data for evidence analysis and better visualization. Solid modeling tools such as interactive cut planes, zooming, rotation, mirroring, scalable captions, labels, grids, marking, measurement of spatial distances, area and volume measurements, animation, rendering, coloring, and texturing enables qualitative and qualitative comparisons of 2D impressions and also enable the usage of reconstructed models in virtual reality visualization and related technology in fast and accurate manner. Moreover, the physical reconstruction of 2D impressions using 3D printing offers a realistic visual representation of the object and facilitates tactile exploration. This aids in evaluating the similarity between impression evidence and corresponding known prints or footwear. For latent impression reconstruction, the FDM-printed latent fingerprint impression are illustrated in Figure 24. It was observed that, the three mean fingerprint features including ridge ending, bifurcation, and the island in addition to other individual characteristics including islands, delta, scratch and core are successfully reproduced in the scaled up FDM-printed fingerprint (Figure 24b). However, all features failed to be reproduced in life size (see red circle in Figure 24b), due to the limitation in x-y resolution of the FDM technique in capturing small details, in addition to the stair-case phenomenon inherent with FDM which increase the surface roughness of the replica as discussed earlier. One solution of the resolution drawback of FDM in reproducing real scale fingerprint impression is to use other high resolution 3D printing technologies like SLA, DLP and polyjet. Another solution is the indirect printing of fingerprints through printing the 3D thumb model and use it as a pattern for casting process. Further, next generation contactless 3D fingerprint scanners can now generate high accurate real size 3D model enabling the 3D printing of actual topography of the 3D fingerprint intricate morphological features such as pores, lakes, ridges and valleys. using of advanced micro- and nano-3D printing techniques. Although only fingerprints are used here as a representative example of latent prints, other latent prints can be used in the proposed pipeline. Figure 23: Surface quality of the as-built FDMed plastic impressions: (**a**) 3D printed outside plastic impression; (**b**) Enlarged view showing the free-form nature of 3D printed outside impression surface with different inclination of the sidewall and near-flat surfaces; and (**c**) representation of corresponding stair-step effect inherent to FDM at different build inclinations. For 2D visible impression, Figure 25 shows an FDM-printed model of 2D visible impression of a known footwear in real size. Both main structural features and pressure and wear areas of the outside are clearly replicated. Luminance of each pixel in the impression image which represents the intensity pattern of impression-substrate contact areas are interpreted as local depth of the 3D printed pattern. Another case of FDM-printed model of 2D visible impression of unknown footwear is illustrated in Figure 26. Details also were successfully reproduced. Inverted 3D morphology of the insole may increase rendering efficiency and are also its corresponding 3D printed can be use as additional visualization aid as shown in Figure 26d. Figure 24: FDM-printed latent fingerprint impression: (**a**) fingerprint reference image (adopted from [PERSON] et al. [29] with permission from Elsevier); (**b**) corresponding FDM-printed fingerprint replica in scaled up and life sizes. (Scale bar: 30 mm).