A image detector comprises a light source for radiating light in accordance with a predetermined signal; a window for transmitting the light from the light source; a thin film phototransistor for generating an optical current in accordance with the intensity of external light; a storage capacitor for storing charge information transmitted from the thin film phototransistor; a thin film switching transistor for outputting the information stored in the storage capacitor in accordance with an external control signal; an insulating layer for covering the window, the thin film phototransistor, the storage capacitor, and the thin film switching transistor; a protecting layer formed on the insulating layer; and a conductive object detection pattern formed on the protecting layer to apply an electrical power supply signal to the light source when a conductive living object contacts the conductive objecting detecting pattern.