A Survey on Banknote Recognition Methods by Various Sensors
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sensors Review A Survey on Banknote Recognition Methods by Various Sensors Ji Woo Lee, Hyung Gil Hong, Ki Wan Kim and Kang Ryoung Park * Division of Electronics and Electrical Engineering, Dongguk University, 30 Pildong-ro 1-gil, Jung-gu, Seoul 100-715, Korea; [email protected] (J.W.L.); [email protected] (H.G.H.); [email protected] (K.W.K.) * Correspondence: [email protected]; Tel.: +82-10-3111-7022; Fax: +82-2-2277-8735 Academic Editor: Vittorio M. N. Passaro Received: 5 January 2017; Accepted: 4 February 2017; Published: 8 February 2017 Abstract: Despite a decrease in the use of currency due to the recent growth in the use of electronic financial transactions, real money transactions remain very important in the global market. While performing transactions with real money, touching and counting notes by hand, is still a common practice in daily life, various types of automated machines, such as ATMs and banknote counters, are essential for large-scale and safe transactions. This paper presents studies that have been conducted in four major areas of research (banknote recognition, counterfeit banknote detection, serial number recognition, and fitness classification) in the accurate banknote recognition field by various sensors in such automated machines, and describes the advantages and drawbacks of the methods presented in those studies. While to a limited extent some surveys have been presented in previous studies in the areas of banknote recognition or counterfeit banknote recognition, this paper is the first of its kind to review all four areas. Techniques used in each of the four areas recognize banknote information (denomination, serial number, authenticity, and physical condition) based on image or sensor data, and are actually applied to banknote processing machines across the world. This study also describes the technological challenges faced by such banknote recognition techniques and presents future directions of research to overcome them. Keywords: banknote recognition; counterfeit banknote detection; serial number recognition; fitness classification; various sensors 1. Introduction 1.1. Motivation of the Research Despite a decrease in the use of currency due to the recent global expansion in electronic financial transactions, transactions in real money continue to be very important in the global market [1]. While performing transactions in real money, touching and counting notes by hand is still a common practice in daily life, but the use of various types of automated machines has become essential for large-scale and safe transactions. Such automated self-service machines include automated teller machines (ATMs) for money deposits and withdrawals, as well as financial transactions [2], banknote counters [3] and coin counters [4], mostly used in banks, and automatic vending machines, into which money is inserted to purchase goods [5]. These devices must be equipped with four essential functions: banknote recognition, counterfeit banknote detection, serial number recognition, and fitness classification. While limited surveys have been conducted in previous studies on the areas of banknote recognition and counterfeit banknote recognition, this paper is the first survey of its kind to review all four areas. This lack of research is ascribable to the fact that banknote recognition studies have been mostly carried out in industrial settings rather than for academic purposes. In this study, Sensors 2017, 17, 313; doi:10.3390/s17020313 www.mdpi.com/journal/sensors Sensors 2017, 17, 313 2 of 34 Sensors 2017, 17, 313 2 of 32 Sensors 2017, 17, 313 2 of 32 different methods related to the four aforementioned areas used therein are analyzed, and future previousdifferent studiesmethods and related the advantages to the four and aforementi disadvantagesoned areas of the used different therein methods are analyzed, related and to the future four applications are also presented. aforementionedapplications are areasalso presented. used therein are analyzed, and future applications are also presented. 1.2. Scope and Method of Our Research 1.2.1. Scope of Our Research This paperpaper presents presents methodologies methodologies for recognizingfor recognizing banknotes banknotes in the in four the main four categories main categories of banknote of recognition,banknote recognition, counterfeit counterfeit banknote banknote detection, detection, serial number serial number recognition, recognition, and fitness and fitness classification. classification. BanknoteBanknote recognition recognition generally generally concerns concerns classification classification of bankno of banknotestes by denomination, by denomination, i.e., i.e.,the thecurrency currency amount amount of a note of a of note a specific of a specific country. country. This classification This classification also enables also recognition enables recognition of the year of theprinting year of and printing input and direction input direction of the ofclassified the classified denomination. denomination. In some In some studies, studies, the the scope scope of recognition is extended to simultaneous recognition of two or more national currencies. Technologies Technologies for banknote recognition areare describeddescribed inin detaildetail inin SectionSection2 2.. Counterfeit banknote detection generally concernsconcerns methods for distinguishing between genuine and fake notes. As shown in the example of a genu genuineine and a counterfeit USD 100 bill in Figure 11a,b,a,b, respectively, aa validationvalidation checkcheck isis donedone byby examiningexamining anti-counterfeiting features.features. Section3 3 describes describes technologies for counterfeit banknotebanknote detectiondetection inin detail.detail. (a) (b) Figure 1. Example of genuine and counterfeit banknotes (USD 100 bill): (a) a genuine banknote; Figure 1.1. ExampleExampleof of genuine genuine and and counterfeit counterfeit banknotes banknotes (USD (USD 100 100 bill): bill): (a) a(a genuine) a genuine banknote; banknote; (b) a (b) a counterfeit banknote. counterfeit(b) a counterfeit banknote. banknote. A banknote serial number is a unique alphanumerical identifier engraved on each banknote in the A banknote serial number is a unique alphanumer alphanumericalical identifieridentifier engraved on each banknote in the banknote production process. It contains the name of the issuing bank and serial information of each banknote production process. It contains the name of the issuing bank and serial information of each denomination [6]; Figure 2 shows the serial number of a USD 100 bill. Since each banknote has its own denomination [[6];6]; Figure2 2 shows shows thethe serialserial numbernumber ofof aa USDUSD 100100 bill.bill. SinceSince eacheach banknotebanknote hashas itsits ownown unique serial number, it can be used to trace its source and circulation route and can thus be efficiently unique serial number, it can be used to trace its sour sourcece and circulation route and can thus be efficiently efficiently used to detect counterfeit banknotes. Related technologies are described in detail in Section 4. used to detect counterfeit banknotes. banknotes. Related Related te technologieschnologies are are described described in in detail detail in in Section Section 4.4 . Figure 2. Example of serial number code (USD 100 bill). Figure 2. Example of serial number code (USD 100 bill). Sensors 2017, 17, 313 3 of 34 Sensors 2017, 17, 313 3 of 32 Fitness classificationclassification of of banknotes banknotes generally generally concerns concerns methods methods for classifying for classifying banknotes banknotes according toaccording their physical to their conditions, physical conditions, such as soiling. such Asas soil showning. inAs the shown example in the of example two INR of 10 two bills INR in Figure 10 bills3, banknotesin Figure 3, of banknotes the same of denomination the same denomination may exhibit may fit or exhibit unfit conditions, fit or unfit whichconditions, include which soiling include and creasessoiling and (Figure creases3a), depending(Figure 3a), on depending circulation on intensity circulation and intensity climate conditions.and climate In conditions. order to maintain In order theto maintain fitness of the banknotes fitness of in banknotes circulation, in automatedcirculation, self-serviceautomated self-service terminals, suchterminals, as ATMs, such need as ATMs, to be equippedneed to be with equipped a fitness with classification a fitness classification function to sort fu outnction and to retrieve sort out unfit and banknotes. retrieve unfit Retrieving banknotes. unfit banknotesRetrieving isunfit also banknotes necessary foris also preventing necessary banknote for preventing classification banknote errors. classification Fitness classification-related errors. Fitness technologiesclassification-related are described technologies in detail are in described Section5. in detail in Section 5. (a) (b) Figure 3. Example of unfit unfit and fitfit banknotes (INR 10 bill): (a) UnfitUnfit banknote; ((b)) FitFit banknote.banknote. 1.2.2. Method of Our Research 1.2.2. Method of Our Research Figure 4 presents a typical process flow of banknote recognition implemented in a self-service Figure4 presents a typical process flow of banknote recognition implemented in a self-service terminal. An input banknote is scanned by a sensor to discern the image and other data necessary for terminal. An input banknote is scanned by a sensor to discern the image and other data necessary for recognizing its denomination and anti-counterfeiting