Handwritten Signature Verification (HSV)

Introduction

Holographic signature is probably one of the most ancient ways to authenticate and express their will, for example in constitutions and marriages. Even before other modern methods were invented, signatures were already culturally accepted and understood.

It is important to make it clear the difference between validation and authentication. Validation verifies that the information provided matches previously recorded data. Authentication checks identity against certain previously declared biographic information. It mainly verifies the identity that the person declares; it does not infer identity from current data.

There are several approaches to verify identity, including iris and fingerprint scanning. However handwriting is still the most prevalent and natural way to do it. Common security and validation approaches include the ones depicted in Table 1.

From the table, is simple to observe that high accuracy is often in invasive approaches cases and at a high cost.

The signature approach is non-invasive, and the rate of false positives is lower than using other fingerprint techniques. As a consequence, it is a good option to perform a quick and easy light validation. Furthermore, validation is a faster process than identification. For this reason, it is more commonly used.

Biometric authentication has been widely used as a trusted security solution in protecting sensitive asset. These systems are not based on what a person possesses (password, PIN, token), but on the basis of what the person “is”. Unlike physiologic biometry, the authentication with holographic signature is non-intrusive. For hundreds of years, the signature has been approved by all cultures and civilizations with a major social implication, and it has been accepted as legal evidence.

Nature of Handwritten Signatures

It is well known that doesn’t exist two signatures equals of the same person. Successive signatures by the same person will differ, may also differ in scale and orientation. For example signatures written with a strange pen and in an unaccustomed place are likely to be different than the normal signatures of an individual. When a signature is being written to be used for comparison, this can also produce a self-conscious, unnatural signature.

Some researchers suggests that a signature has at least three attributes, form, movement and variation, and since signatures are produced by moving a pen on paper, movement perhaps is the most important part of a signature.

The movement to signature is produced by muscles of the fingers, hand, wrist, and for some writers the arm, and these muscles are controlled by nerve impulses. Once a person is used to signing his or her signature, these nerve impulses are controlled by the brain without any particular attention to detail.

Basic HSV Methodology

Most HSV techniques use the following procedure for performance evaluation:

1. Registration - Obtain a number of signatures for each individual at enrolment or registration time (these signatures are called sample signature).
2. Pre-processing and Building Reference Signature(s) - pre-process the sample signatures if required, compute the features required, and produce one or more reference signatures. Decide on what threshold will be used in verifying a signature.
3. Test Signature - when a user wishes to be authenticated, he/she presents the identification of the individual he/she claims to be and presents a signature (we call this signature the test signature). Pre-process as in Step 2 and compute the features of the signature.
4. Comparison Processing - the test signature is compared with the reference signature(s) based on the features’ values and the difference between the two is then computed using one of the many existing (or specially developed) distance measures.

Architecture

Capture signature

Validate signature

HSV Applications

A typical on-line HSV system will of course require that a signature input device like a graphics tablet be connected to each workstation to capture signature details. This technique has the potential to replace the password mechanisms for accessing computer systems in some situations. The major disadvantage of this approach of course is the requirement that a graphics tablet be attached to each workstation.

Reliable HSV could well have other applications. For example, it might assist in reducing the forging of passports. There is considerable opposition to such a move in many countries. HSV could be a more acceptable approach since an application for a passport normally requires that the applicant go to some authorized office to file an application form and that signatures be certified in the presence of an authorized officer.

It is thus not unreasonable that the office where a passport application is filed might require the applicant to provide a set of sample signatures, which would be captured electronically and used for building a reference signature. That reference signature could then be placed on a magnetic strip on the passport (passports are likely to feature magnetic strips for faster processing any way). At the port of entry, the person entering a country would then be required to sign his or her name on a graphics tablet and the signature would be compared with the reference signature on the passport strip. Forging of passports would then be almost impossible.

HSV Products

Communication Intelligence Corporation (CIC, www.cic.com) appears to have a number of signature verification products. A product called Sign-On, it is claimed, allows HSV to be built-in to a variety of widely used software enabling the system to use a handwritten signature instead of a password. It uses not only the signature image, but acceleration, stroke angles, start and stop pressures (if available) and other factors. The signature information can be updated each time a successful verification occurs. The product uses six signatures plus a final verifying signature to build a reference signature. The test signature is then compared with the reference signature resulting in one of three judgments: true, forgery or ambiguous. The product is claimed to have a 2.5% ERR but details of its performance evaluation are not available.

SiSign from SiVault Systems (www.sivault.com/solutions/sisign.html) uses the standard HSV procedure that requires registration. It is suggested that registration could be done at a point of sale terminal if the customer has another reliable form of identification (for example, a driver’s license). A signature captured by a pressure-sensitive mobile phone may also be used.

IBM Israel (www.haifa.il.ibm/projects/image/sv) has an HSV product that claims a total error rate of 1.5%. It follows the usual HSV procedure in requiring user enrolment. It is claimed that the reference signature can be stored using only 100-150 bytes of storage. WonderNet, an Israeli company, has a number of products that use HSV techniques for including handwritten signatures in documents. The HSV procedure uses three sample signatures to build a reference signature that is used for verifying test signatures. The system modifies the reference signature each time a signature is authenticated.

BioSig from Vector Intelligence is an on-line HSV system developed by Lucent Bell Labs. It is based on three patents. The software uses a technique that divides the signature into a sequence of line segments which are ordered according to the time sequence of the signature. Each segment is assigned a stroke direction value that depends upon the orientation of the segment. It also captures 23 features including speed and stroke direction. A verification score is then found and the signature is accepted or rejected based on that score. An error rate of 1.2% is claimed.

Author

- Author

References

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http://biometrics.pbworks.com/w/page/14811349/Advantages-and-disadvantages-of-technologies
- Validación de Firmas Ológrafas by Tamara D. Blum, Ariel J. Sztern and Daniela López De Luise, Universidad de Palermo, AIGroup
- GUPTA, G.K. The State of the Art in On-line Handwritten Signature Verification, Faculty of Information Technology, Monash University, Building 75, Clayton, Victoria 3800, Australia (2006).
- PLAMONDON, R. The Design of an On-line Signature Verification System: From Theory to Practice, Int Journal of Patt Rec and Art Int, 8, 3, (1994), 795-811.
- PLAMONDON, R., and LORETTE, G. Automatic Signature Verification and Writer Identification — The State of the Art. Pattern Recognition, 22, (1989), 107-131.

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