Online Signature Verification and Recognition: An Approach Based on Symbolic Representation

In this paper, we propose a new method of representing on-line signatures by interval valued symbolic features. Global features of on-line signatures are used to form an interval valued feature vectors. Methods for signature verification and recognition based on the symbolic representation are also proposed. We exploit the notions of writer dependent threshold and introduce the concept of feature dependent threshold to achieve a significant reduction in equal error rate. Several experiments are conducted to demonstrate the ability of the proposed scheme in discriminating the genuine signatures from the forgeries. We investigate the feasibility of the proposed representation scheme for signature verification and also signature recognition using all 16500 signatures from 330 individuals of the MCYT bimodal biometric database. Further, extensive experimentations are conducted to evaluate the performance of the proposed methods by projecting features onto Eigenspace and Fisherspace. Unlike other existing signature verification methods, the proposed method is simple and efficient. The results of the experimentations reveal that the proposed scheme outperforms several other existing verification methods including the state-of-the-art method for signature verification.     

On using the Viterbi path along with HMM likelihood information for online signature verification.

This paper describes a system using two complementary sorts of information issuing from a hidden Markov model (HMM) for online signature verification. At each point of the signature, 25 features are extracted. These features are normalized before training and testing in order to improve the performance of the system. This normalization is writer-dependent; it exploits only five genuine signatures used to train the writer HMM. A claimed identity is confirmed when the arithmetic mean of two similarity scores, obtained on an input signature, is higher than a threshold. The first score is related to the likelihood given by the HMM of the claimed identity; the second score is related to the segmentation given by such an HMM on the input signature. A personalized score normalization is also proposed before fusion. Our approach is evaluated on several online signature databases, such as BIOMET, PHILIPS, MCYT, and SVC2004, which were captured under different acquisition conditions. For the first time in signature verification, we show that the fusion of segmentation-based information generated by the HMM with likelihood-based information considerably improves the quality of the verification system. Finally, owing to our two-stage normalization (at the feature and score levels), we show that our system results in more stable client-score distributions across databases and in a better separation between the distributions of client and impostor scores.     

用于在线签名认证的特征提取和个性化特征选择方法

提出一种在线签名认证中的特征提取和特征选择的方法.采用一种F-Tablet手写板采集签名数据.该手写板的特点是不仅可记录签名时的字形信息(x,y)序列,还可记录签名时的五维力信息(F_x,F_y,F_z,M_x,M_y)序列.从每个签名中提取3个等级共188个特征,接着定义特征重要性函数F,然后根据特征的重要性函数F的值对选取的188个特征进行排序,对F设不同的阈值就可完成不同的特征选择.在认证过程中使用SVM算法对选取的特征进行训练,然后用训练所得的模型进行验证.该方法的错误拒绝率为1.2%,错误接受率为3.7%.     

A Markov chain Monte Carlo algorithm for bayesian dynamic signature verification

Authentication of handwritten signatures is becoming increasingly important. With a rapid increase in the number of people who access Tablet PCs and PDAs, online signature verification is one of the most promising techniques for signature verification. This paper proposes a new algorithm that performs a Monte Carlo based Bayesian scheme for online signature verification. The new algorithm consists of a learning phase and a testing phase. In the learning phase, semi-parametric models are trained using the Markov Chain Monte Carlo (MCMC) technique to draw posterior samples of the parameters involved. In the testing phase, these samples are used to evaluate the probability that a signature is genuine. The proposed algorithm achieved an EER of 1.2% against the MCYT signature corpus where random forgeries are used for learning and skilled forgeries are used for evaluation. An experimental result is also reported with skilled forgery data for learning.     

Wavelet-Based Off-Line Handwritten Signature Verification

In this paper, a wavelet-based off-line handwritten signature verification system is proposed. The proposed system can automatically identify useful and common features which consistently exist within different signatures of the same person and, based on these features, verify whether a signature is a forgery or not. The system starts with a closed-contour tracing algorithm. The curvature data of the traced closed contours are decomposed into multiresolutional signals using wavelet transforms. Then the zero-crossings corresponding to the curvature data are extracted as features for matching. Moreover, a statistical measurement is devised to decide systematically which closed contours and their associated frequency data of a writer are most stable and discriminating. Based on these data, the optimal threshold value which controls the accuracy of the feature extraction process is calculated. The proposed approach can be applied to both on-line and off-line signature verification systems. Experimental results show that the average success rates for English signatures and Chinese signatures are 92.57% and 93.68%, respectively.     

On-line signature verification

We describe a method for on-line handwritten signature verification. The signatures are acquired using a digitizing tablet which captures both dynamic and spatial information of the writing. After preprocessing the signature, several features are extracted. The authenticity of a writer is determined by comparing an input signature to a stored reference set (template) consisting of three signatures. The similarity between an input signature and the reference set is computed using string matching and the similarity value is compared to a threshold. Several approaches for obtaining the optimal threshold value from the reference set are investigated. The best result yields a false reject rate of 2.8% and a false accept rate of 1.6%. Experiments on a database containing a total of 1232 signatures of 102 individuals show that writer-dependent thresholds yield better results than using a common threshold.     

HMM-based on-line signature verification: Feature extraction and signature modeling

A function-based approach to on-line signature verification is presented. The system uses a set of time sequences and Hidden Markov Models (HMMs). Development and evaluation experiments are reported on a subcorpus of the MCYT bimodal biometric database comprising more than 7000 signatures from 145 subjects. The system is compared to other state-of-the-art systems based on the results of the First International Signature Verification Competition (SVC 2004). A number of practical findings related to feature extraction and modeling are obtained.     

Signature Verification: Increasing Performance by a Multi-Stage System

A serial three stage multi-expert system for facing the problem of signature verification is proposed. The whole decision process is organised into successive stages, each using a very reduced set of features for recognising forgeries and providing information about the reliability of the recognition process. The first expert, adopting only a single global feature, is devoted to the elimination of random and simple forgeries. The second stage receives only those signatures not classified as false by the first stage (i.e. those signatures really genuine or forgeries reproduced in a skilled way), and adopts a single specific feature suitable for isolating skilled forgeries. Both of these two stages employ suitable criteria for estimating the reliability of the performed classification, so that, in case of uncertainty, the signature is forwarded to a final stage which takes the final decision, taking into account the decisions of the previous stages together with the corresponding reliability estimations. The proposed multi-stage automatic signature verification system has been tested on a database of signatures produced by 49 different writers. The experimental analysis highlights the effectiveness of the approach: the proposed system employing only two features, used in distinct moments of the decision process, performs better than other systems, employing larger feature set (including the features used in the proposed system) and performing classification in a single stage.     

基于几何中心静态手写签名的识别算法研究*

研究了静态手写体签名识别和认证的问题。针对静态手写体签名无法提供笔画之间前后时序动态信息和手写笔画的压力信息,提出了一种利用手写签名的几何中心作为特征值的识别和认证算法。首先将静态签名图像依据几何中心不断进行切分,使其成为独立的小块;然后依据各个小块的几何中心的相对位置和距离提取特征值;在此基础上进行签名识别和认证。实验结果显示本方法快速有效,所提取的特征能稳定地描述包含集合形变的手写签名字体。该方法能拓展应用到手写体的识别系统中。     

Off-line signature verification and forgery detection using fuzzy modeling

Automatic signature verification is a well-established and an active area of research with numerous applications such as bank check verification, ATM access, etc. This paper proposes a novel approach to the problem of automatic off-line signature verification and forgery detection. The proposed approach is based on fuzzy modeling that employs the Takagi-Sugeno (TS) model. Signature verification and forgery detection are carried out using angle features extracted from box approach. Each feature corresponds to a fuzzy set. The features are fuzzified by an exponential membership function involved in the TS model, which is modified to include structural parameters. The structural parameters are devised to take account of possible variations due to handwriting styles and to reflect moods. The membership functions constitute weights in the TS model. The optimization of the output of the TS model with respect to the structural parameters yields the solution for the parameters. We have also derived two TS models by considering a rule for each input feature in the first formulation (Multiple rules) and by considering a single rule for all input features in the second formulation. In this work, we have found that TS model with multiple rules is better than TS model with single rule for detecting three types of forgeries; random, skilled and unskilled from a large database of sample signatures in addition to verifying genuine signatures. We have also devised three approaches, viz., an innovative approach and two intuitive approaches using the TS model with multiple rules for improved performance.     

Online signature verification based on signatures turning angle representation using longest common subsequence matching

Online signature verification has been intensively investigated in several directions, such as the selected feature(s), similarity estimation and classification method. Local feature approaches combined with elastic distance metrics have the most successful performance so far. The Turning Angle Sequence (TAS) feature has not been extensively explored for signature verification, while the fusion of TASs of different scales, the Turning Angle Scale Space (TASS) is a new approach in this field. In this paper, we study the signatures TAS and TASS representations and their application to online signature verification. In the matching stage, a variation of the longest common sub-sequence matching technique has been employed. Experimental results using varying TAS(S) representation parameters on two publicly available signature databases, the SVC2004 and SUSIG, show the improved performance of the selected feature along with the chosen elastic distance measure on the equal error rate results of the online signature verification task.     

Online handwritten signature verification based on association of curvature and torsion feature with Hausdorff distance

The paper presents an efficient on-line signature verification method based on the dynamic features of a given signature. In the proposed approach, curvature and torsion feature are associated with Hausdorff distance measure which can be used in the verification process. In the feature extraction step, the signature trajectory is approximated as a spatial curve. A set of curvature and torsion value of extreme point is computed from both x coordinate, y coordinate and pressure feature so that the dimension of the curve is reduced. Therefore, a new composed signature feature is created for each person. For the obtained feature data, the most distinctive Hausdorff distance is further proposed to calculate the distances of the eight-dimensional feature vector between the test signature and corresponding template signatures for the verification of the test sample. Comprehensive experiments are implemented on three publicly available databases: the SVC2004, SUSIG and MCYT-100 database. A comparison of our results with some recent signature verification methods available in the literature is provided with equal error rate, and the results indicate that the proposed method would better recognize genuine signatures, random and skilled forgeries.

     

Online signature verification based on null component analysis and principal component analysis

This paper describes a method for stroke-based online signature verification using null component analysis (NCA) and principal component analysis (PCA). After the segmentation and flexible matching of the signature, we extract stable segments from each reference signature in order that the segment sequences have the same length. The reference set of feature vectors are transformed and separated into null components (NCs) and principal components (PCs) by K-L transform. Online signature verification is a special two-category classification problem and there is not a single available forgery set in an actual system. Therefore, it is different from the typical application of PCA in pattern recognition that both NCA and PCA are used to respectively analyze stable and unstable components of genuine reference set. Experiments on a data set containing a total 1,410 signatures of 94 signers show that the NCA/PCA-based online signature verification method can achieve better results. The best result yields an equal error rate of 1.9%.     

On-line signature verification system with failure to enrol management

In this paper we introduce a new biometric verification system based on on-line signatures and simulate its operation. For this purpose we have split the MCYT signature database in three subsets: one for classifier training, another for system adjustment and a third one for system testing simulating enrolment and verification. This context corresponds to a real operation, where a new user tries to enrol an existing system and must be automatically guided by the system in order to detect the failure to enrol (FTE) situations. The main contribution of this work is the management of FTE situations by means of a new proposal, called intelligent enrolment, which consists of consistency checking in order to automatically reject low quality samples. This strategy enhances the performance of the system to 22% when 8% of the users are left out. In this situation 8% of the people cannot be enroled in the system and must be verified by other biometrics or by human abilities. These people are identified with intelligent enrolment and the situation can be thus managed. In addition we also propose a DCT-based feature extractor with threshold coding and discriminability criteria.     

Legendre polynomials based feature extraction for online signature verification. Consistency analysis of feature combinations

In this paper, feature combinations associated with the most commonly used time functions related to the signing process are analyzed, in order to provide some insight on their actual discriminative power for online signature verification. A consistency factor is defined to quantify the discriminative power of these different feature combinations. A fixed-length representation of the time functions associated with the signatures, based on Legendre polynomials series expansions, is proposed. The expansion coefficients in these series are used as features to model the signatures. Two different signature styles, namely, Western and Chinese, from a publicly available Signature Database are considered to evaluate the performance of the verification system. Two state-of-the-art classifiers, namely, Support Vector Machines and Random Forests are used in the verification experiments. Error rates comparable to the ones reported over the same signature datasets in a recent Signature Verification Competition, show the potential of the proposed approach. The experimental results, also show that there is a good correlation between the consistency factor and the verification errors, suggesting that consistency values could be used to select the optimal feature combination.     

A Hidden Markov Model approach to online handwritten signature verification

A method for the automatic verification of online handwritten signatures using both global and local features is described. The global and local features capture various aspects of signature shape and dynamics of signature production. We demonstrate that adding a local feature based on the signature likelihood obtained from Hidden Markov Models (HMM), to the global features of a signature, significantly improves the performance of verification. The current version of the program has 2.5% equal error rate. At the 1% false rejection (FR) point, the addition of the local information to the algorithm with only global features reduced the false acceptance (FA) rate from 13% to 5%. Received June 27, 1997/ Revised October 31, 1997     

基于曲线分段相似匹配的在线签名认证

针对在线签名认证过程中出现的误匹配问题和曲线的缩放、旋转、位移以及采样不均匀导致的匹配距离过大的问题，提出一种基于曲线分段相似匹配的方法。在进行在线签名认证时，首先对两签名曲线进行分段粗匹配，主要应用了一种基于窗口累计差异矩阵的动态规划算法得到匹配关系。然后，对匹配对计算相似距离和加权累加和，主要方法是对曲线段进行拟合，在一定范围内进行相似变换，对其重采样并计算匹配对的欧氏距离。最后，取测试签名和所有模板签名的相似距离的平均值作为认证距离，将其与训练的阈值进行比较，从而判定真伪。在公开数据库SUSIG的Visual数据集和Blind数据集对该方法进行了测试，使用个性化阈值时分别可以得到3.56%和2.44%的等误率。所提方法在Blind数据集上的等误率比传统的动态时间规划（DTW）方法降低了约14.4%。实验结果表明，对熟练伪造签名和随机伪造签名的认证效果具有一定的优势。     

On-line signature verification using LPC cepstrum and neuralnetworks

An on-line signature verification scheme based on linear prediction coding (LPC) cepstrum and neural networks is proposed. Cepstral coefficients derived from linear predictor coefficients of the writing trajectories are calculated as the features of the signatures. These coefficients are used as inputs to the neural networks. A number of single-output multilayer perceptrons (MLPs), as many as the number of words in the signature, are equipped for each registered person to verify the input signature. If the summation of output values of all MLPs is larger than the verification threshold, the input signature is regarded as a genuine signature; otherwise, the input signature is a forgery. Simulations show that this scheme can detect the genuineness of the input signatures from a test database with an error rate as low as 4%     

基于HMM/DTW两级结构的签名认证方法

提出一种基于HMM和DTW在线手写签名认证方法的改进方法。该方法使用签名关键点和关键点的特征值进行签名的状态划分和状态匹配,实现类内签名状态划分的一致性。并利用在线手写签名二维信息的DTW距离作为签名隐马尔科夫模型的状态观测值,构建二级签名隐马尔科夫模型认证框架进行签名认证,得到较好的认证效果。实验结果表明,认证的准确率能达到93%左右。