2. The image reading apparatus according to claim 1 , further comprising: a document-size calculator for calculating a size of the document; an ultrasonic sensor for receiving an ultrasonic wave which passes the document; and an infrared sensor for receiving an infrared ray reflected from the document, wherein the document-type identification module identifies the type of the document based on the size of the document, an intensity of the ultrasonic wave received by the ultrasonic sensor, and an intensity of the infrared ray received by the infrared sensor.
2. The image reading apparatus according to claim 1 , further comprising: a document-size calculator for calculating a size of the document; an ultrasonic sensor for receiving an ultrasonic wave which passes the document; and an infrared sensor for receiving an infrared ray reflected from the document, wherein the document-type identification module identifies the type of the document based on the size of the document, an intensity of the ultrasonic wave received by the ultrasonic sensor, and an intensity of the infrared ray received by the infrared sensor. 3. The image reading apparatus according to claim 2 , wherein the document-type identification module identifies the plastic card as the type of the document, when the size of the document is equal to or smaller than a first predetermined size, and when the intensity of the ultrasonic wave received by the ultrasonic sensor is lower than a first predetermined value or the intensity of the infrared ray received by the infrared sensor is equal to or higher than a second predetermined value.