An image sensing device includes an image sensor that converts incident light into a first image by operating the image sensor under a first exposure time and a second image by operating the image sensor under a second exposure time which is different from the first exposure time; a calculation circuit to receive the first image and generate a third image corresponding to the second image based on the first image and a exposure ratio between the first and the second exposure times; a combination circuit to combine the second image and the third image to generate a combination image; a conversion circuit to convert or maintain each code value of the combination image to have the same bit depth based on the combination image and the exposure ratio; and a memory circuit coupled to the conversion circuit to store image values outputted from the conversion circuit.