# Towards Facial Biometrics for ID Document Validation in Mobile Devices
## 1 Introduction
The choice of MRC and encoding strategy is provided by the requirement that the bona fide MRC cannot be generated by an unauthorized issuer, which complicates producing fraudulent identification documents for deceitful impersonating. The validation of such document is performed by extracting two biometric templates from the frontal face photo and the MRC which are printed on its exterior. The templates are compared to determine if they belong to the same identity. The pipeline of the process in such a match-on-document scenario does not require network access, and the validation may be performed totally offline. However, the proposed approach in practical applications  
Figure 1: Pipeline of the proposed system: (**a**) ID card generating; and (**b**) ID card validating. indeed may be expanded straightforwardly by including biographic data (name, date of birth, etc.) into the MRC. It should be pointed out that the formulation of the face recognition problem in our method is specific. The main task being solved is to protect the particular instance of the issued document at the moment of its personalization with variable data. With this formulation, we do not focus on matching several photos of a single identity, although the designed method may be expanded for deployment in such a scenario. That is stated due to the fact that any newly issued document will contain the secured encoded biometric template, which corresponds to the particular face image to be printed on this document. However, in the scope of this work, the mentioned limitation is provided only by the choice of the training and test datasets. That is why we clarify the formulation of a problem as the protection of the particular face image of the ID document from various biometric impostor attacks. Furthermore, one must notice that the matching between the two templates is not expected to be a perfect one, since the minutiae extracted from the frontal face are always different each time the validation occurs, due to image color and radiometric distortion, lighting conditions and the camera's intrinsic and extrinsic parameters, thus complicating the problem of matching different identities. Summing up, the research and development of security solutions for match-on document scenario is important and for instance have been performed in our initial study [5]. In this work, which is the extended version of the paper presented at the BIOSIG2020 conference, we continue this investigation towards a compact offline mobile solution to secure ID and travel documents. By employing the secured MRC to embed the ID document with a carefully designed facial descriptor, we perform the document validation without storing biometric samples and templates in the remote database. In comparison with the previous work, we modify the facial biometric template by including texture components. Our implementation of the facial descriptor is compact and optimized for usage in mobile devices. We also estimate the effect of template compression following the concept of match-on-document verification. Finally, we present several collected print/capture datasets which may be useful for analyzing the performance. The paper is organized in the following way. In Section 2, we review some recently published works related to our research. Section 3 represents the discussion of the improved face descriptor implementation approach of differential validating and compressing the designed descriptors. Section 4 is devoted to the choice and application of machine-readable code (MRC) to our work. In Section 5, we present the details of the acquired in-house datasets. The discussion on the experimental results is performed in Section 6.