An image-sensing system for the efficient detection of defective pixels is shown. An arithmetic logic unit (ALU) determines a defective pixel candidate of an image sensor based on the first frame captured by the image sensor, performs a lower-part comparison on the defective pixel candidate based on the first frame, and performs an upper-part comparison on the defective pixel candidate based on the second frame captured by the image sensor. The defective pixel candidate is confirmed to be defective based on the first frame as well as the second frame. Only limited pixel data is buffered for the defective pixel detection.