**Biometric system can work in two modes:**

Identification either in identification mode or verification mode. Identification mode works as one to many by comparing the individual with all the templates stored in the dataset, while a verification mode works as one to one by comparing the individual with his own template stored in the dataset.

Sanderson and Paliwal et al. [18] divide the fusion into two categories: before classification called pre-matching and after classification called post-matching as shown in **Figure 5**:

A Survey on Soft Biometrics for Human Identification http://dx.doi.org/10.5772/intechopen.76021 43

• Pre-classification fusion [19–21]: before the classification level, the integration can be done

**1.** Sensor level: integrating the raw data is difficult because it has a lot of unimportant features not only the region of interest and data collected from the sensors can be suffered from noisy as nonuniform illumination. Sensor-level fusion refers to raw data obtained using multiple sensors or multiple snapshots of a biometric using a single sensor. Face images collected from multiple sources with different resolutions may

**2.** Feature level: in feature-level fusion, we get a lot of information by producing one feature set from fusing different features that are extracted from the captured images. So feature sets need to be tuned, normalized, transformed, and reduced. In practice, it is difficult to achieve feature-level fusion because concatenating different features

• Post-classification fusion [19–22]: the integration after the classification can be divided into

**1.** At score stage [23]: scores combined to generate one score value to and used for making decision according to the threshold value. Threshold making the system more reliable than using true and false since there is range can be tuned to increase or decrease the false acceptance rate and false rejected rate. However, a lower threshold decreases the rate of falsely rejected rate but also increases the rate of falsely accepted rate.

in two ways as followed:

three types:

**Figure 5.** Fusion levels.

not be possible to integrate together.

may lead to dimensionality problem.
