Thesis - Instituto de Telecomunicações

20 CHAPTER 2. STATE OF THE ARTof handwritten signatures, human verification is normally very accurate in identifying genuinesignatures. Biometric authentication based on on-line handwritten signatures relies onsignature dynamics information to further reduce the possibility of fraud [253].Two formats of handwritten signature have been proposed: off-line, image based, andon-line using the writing dynamics [192, 66]. The first uses the graphical information ofthe signature. The second uses the timing characteristics of the pen stroking, such as thenumber of times the pen goes up and down, and the velocity in the several segments of thesignature [126, 68].In [65], both local and regional information are fused in a final classification, using thedata from the SVC2004 database [252], an EER of 0.15% from non expert forgeries and 6.9% EER for trained expert forgeries are achieved.Advantages and Disadvantages The signature is a well accepted way and the mostfrequently used format to assert identity in our civilian life. The act of providing a signatureis common and the introduction of a technological device is not considered too intrusive.Forgery in an on-line signature verification system can occur if trained persons study theimage and/or the act of signing. Another problem is the failure to access caused by somehealth problems related to the signing hand. It has been noticed that a recently learnedsignature tends to present large intraclass variability and would fail to enroll. The signaturelearning occurs when the signature changes in a marriage situation; when a young adult iscreating the signature for the first time; or simply when the subject decides to change thesignature.2.3.2 VoiceOur voice is influenced by the characteristics of the format of our body, by the physicalconstrains the body produces in the sound wave, and by the temporal characteristics derivedfrom our cognitive processing and timing of sound producing.Speaker recognition via the voice print [44, 15] uses a standard microphone to ask theuser to produce a known sentence, or to say free text sentences [87, 57].Despite some changes to the speaker’s voice due to minor alterations caused by cough