An image acquiring apparatus and image acquiring method are provided. The image acquiring apparatus includes an image sensor for outputting a plurality of first analog image signals corresponding to a plurality of pixels; an ADC for converting the plurality of first analog image signals to a plurality of digital image signals; a DAC for converting the plurality of digital image signals to a plurality of second analog image signals, wherein each of which has an actual voltage value; a comparing unit for respectively comparing the actual voltage values of the plurality of second analog image signals with a reference voltage value so as to generate a plurality of corresponding comparing results; a counting unit for adjusting a counting value according to each of the comparing results; and a control unit for determining whether to stop a scanning operation of the image acquiring apparatus or not according to the counting value.