**5. Conclusions**

We proposed a new capturing device, which is able to acquire finger as well as hand vein images in a fully contactless way. Contactless acquisition has many advantages in terms of hygiene and user acceptance. In addition to the design and technical details of the acquisition device, we also provide a novel, contactless finger and hand vein dataset available for research purposes (can be downloaded here: http://www.wavelab.at/sources/PLUSVein-Contactless/). This dataset is the first available contactless finger vein dataset and one of the first available contactless hand vein datasets. It is a challenging dataset due to the contactless acquisition allowing for more unrestricted finger/hand movement and the resulting finger/hand misplacements. An image quality assessment using three vein tailored metrics has been conducted and confirmed the decent image quality which can be achieved using our proposed capturing device. Moreover, a recognition performance evaluation using several well-established vein recognition schemes has been carried out on this dataset in order to provide baseline results for further research. Those baseline results are competitive for the hand vein data (EER of 0.35%) and within range of other biometric technologies for the finger vein data (EER of 3.66%). Furthermore, biometric sensor level fusion experiments have been conducted to show the additional improvement in the recognition performance which can be achieved by combining finger vein and hand vein data (resulting in an overall best EER of 0.03%).

Our future work includes some improvements on the capturing device itself. The next version of the device should be an embedded device, eliminating the need for an additional PC to control the acquisition process. The capturing device has a built-in touch screen display already which can be used to control it via the graphical user interface. The only thing which is currently missing is the porting of the capturing software to an embedded platform like the Raspberry Pi and the automated start of the capturing process once the data subjects placed their finger/hand. Furthermore, we will extend our contactless finger and hand vein dataset. We are currently acquiring additional subjects and plan to enlarge the dataset to include a total of at least 100 subjects by the end of 2019. Moreover, we aim to do a thorough analysis on which types of finger/hand misplacements are present in the dataset, similar to the work has been done for other finger vein datasets [71]. Based on this analysis we will be able to apply different correction and normalisation schemes in order to improve the recognition performance.

**Author Contributions:** Conceptualization, C.K. and B.P.; methodology, C.K.; software, C.K. and B.P.; validation, C.K. and B.P.; formal analysis, C.K.; investigation, C.K. and B.P.; resources, C.K., B.P. and A.U.; data curation, C.K. and B.P.; writing—original draft preparation, C.K.; writing—review and editing, C.K.; visualization, C.K.; supervision, A.U.; project administration, C.K. and A.U.; funding acquisition, A.U.

**Funding:** This research was funded by European Union's Horizon 2020 research and innovation program under grant agreement number 700259, project PROTECT—Pervasive and UseR Focused BiomeTrics BordEr ProjeCT. This research received further funding by the Austrian Science Fund (FWF) and funding by the Salzburg state government, project no. P32201—Advanced Methods and Applications for Fingervein Recognition. Open Access Funding provided by the Austrian Science Fund (FWF).

**Acknowledgments:** First of all we really appreciate the spent time and effort of all the participants during our data collection and want to express our gratitude for their voluntary participation. Furthermore, we want to thank our colleagues Michael Linortner and Simon Kirchgasser who helped during the data acquisition. The Open Access Funding was kindly provided by the Austrian Science Fund (FWF).

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
