An image sensor system including: a timing control circuit, an image sensor and a modulation circuit. The timing control circuit is arranged to determine if a coding condition is fit according to an input signal and generate a control signal when the coding condition is fit, wherein the input signal is generated in response to each pulse of a clock signal. The image sensor is coupled to the timing control circuit, and the image sensor includes a plurality of pixels, wherein one of the plurality of pixels receives the control signal from the timing control circuit and outputs a sensing signal. The modulation circuit is coupled to the image sensor and arranged to receive the sensing signal and generate an output signal according to the sensing signal, wherein a frequency of the output signal is different from a frequency of the sensing signal.