# Digital Identity in the EU: Promoting eIDAS Solutions Based on Biometrics
## 4 Biometric Identification as a Unique Opportunity
### Enhancing Biometric Verification with 3D  
As discussed above, the main issue with the use of real-world images as probing images is that, individually, they cannot guarantee a sufficient level of accuracy in the verification process. However, rapid progress has been made recently in the field of 3D face reconstruction [33; 34], with the development of novel and powerful algorithms, faster, more accurate, and energy efficient [35], which can obtain impressive results even in the challenging case of reconstruction from a single RGB camera [36; 37]. These techniques are extensively used in forensic applications, particularly for face-based identification, where 3D model reconstruction overcomes the shortcomings of 2D images acquired in crime scenes [38]. The face's geometry is typically modeled as a set of triangles or quad meshes, to which added material properties describe the interaction of the skin with light. Modeling the light surface interactions for a face is an extraordinarily complex task; thus, in some cases, these complexities can be loosened using approximated appearance models with simple reflectance maps and illumination schemes. Furthermore, to allow the reconstruction of the face from images taken in the real world, i.e., in the ill-posed monocular setting, priors that simulate the shape and expression of faces are often used [39; 40]. These priors are typically based on:  
* Blend shape expression models (3D models of a particular fundamental expression);
* Parametric face models (low-dimensional face reconstruction from high-resolution laser scans of hundreds of human faces with neutral expressions). The adoption of these priors not only solves the ill-posed problem but also enables reconstruction results of high quality, as proved by [PERSON] and colleagues [41]. The minimum requirement for the proposed method is to have a standard RGB camera to capture a short video of the face. This means that the method can be applied not only to mobile devices but also to laptops and desktop PCs equipped with a webcam. Another way to reconstruct a 3D model of the face of a person is to use depth cameras. A depth camera is a device that is increasingly used in modern smartphones which can produce a map of distances between the illuminated surfaces and the camera. The measure of each point is based on the time-of-flight (ToF), i.e., the round-trip time of the signal produced by the sensor. Typically, laser or LED lights are used. Every brand produces its specific depth sensor. For example, Apple patented the TrueDepth camera [42], which consists of a traditional camera, an infrared camera, a proximity sensor, and a dot projector, as well as a flood illuminator. This sensor can project more than 30,000 dots, which enablesthe creation of a dense model of the face. The sensor is used mainly for unlocking the smartphone through facial recognition but can also be used for photo editing. Once the 3D model is created, it can be adjusted to correct skin reflectance and mitigate the sources of noise present at the time of the acquisition (poor light conditions, background, small occlusions). Moreover, the pose of the 3D reconstruction can be easily oriented to take a frontal snapshot of the face and use it as a probing image (as depicted in Figure 4). If a mobile device with a depth sensor is used, the 3D reconstruction will be more accurate and can be performed even under poor lighting conditions. A possible implementation of this solution, integrated into the verification scheme of a national eID (for example, the Italian CIE), is depicted in Figure 5.  
The eID authentication scheme is implemented through two distinct macro phases:  
1. Request for the service displayed by the SP's portal/app, which takes place within the user's browser in the domain of the SP;
2. User authentication is performed directly by the IdP. The request to access the eID authentication system takes place through a \"call to action\" made by the SP accessible through a special button.