A Multi-Hypothesis Approach for Off-Line Signature Verification with HMMs

In this paper, an approach based on the combination of discrete hidden Markov models (HMMs) in the ROC space is proposed to improve the performance of off-line signature verification (SV) systems designed from limited and unbalanced training data. This approach is inspired by the multiple-hypothesis principle, and allows the system to choose, from a set of different HMMs, the most suitable solution for a given input sample. By training an ensemble of user-specific HMMs with different number of states, and then combining these models in the ROC space, it is possible to construct a composite ROC curve that provides a more accurate estimation of system´s performance during training and significantly reduces the error rates during operations. The experiments performed by using a real-world SV database with random, simple and skilled forgeries, indicated that the proposed approach can reduce the average error rates by more than 17%.