An image sensor includes a pixel array, a row driver, a detector, an analog-to-digital converter and a controller. The pixel array includes a pixel area including a pixel and a dummy area including a monitoring circuit. The dummy area is disposed on a same substrate as the pixel area. The dummy area is disposed adjacent to the pixel area. The row driver is configured to output a driving signal to the pixel and the monitoring circuit. The detector is configured to receive a monitoring signal from the monitoring circuit. The analog-to-digital converter is configured to receive an analog signal corresponding to an incident light from the pixel and to convert the analog signal to a digital signal. The controller is configured to control the row driver and the analog-to-digital converter.