**Table 2.**

*Advantages of multi-biometric systems.*

• Detection error trade-off (DET) showing error rates on both axes, most often on a logarithmic scale. This curve is plotted for both matching errors and decisions (**Figure 2**).

If we use only one biometric authentication system, the results obtained are not always good enough. Unimodal biometric systems using a single sensor have many limitations, such as lack of uniqueness, universality, and lack of interference level associated with the acquired data, as a result of which they are unable to provide the required level of identification/verification efficiency (**Table 1**). This is due to the fact that the reliability of the biometric modality applied is affected by the precision of a single biometric system (**Table 2**).
