Photodetectors (PDs) as image sensors have been widely used in imaging system due to their outstanding photosensitivity. The improvement of imaging quality (signal-to-noise ratio (SNR)) can be realized by reducing the dark current of PDs. Conventionally, interfacial engineering can effectively suppress the dark current of PDs. Nevertheless, these techniques are hard to be applied in practical imaging systems owing to their complicated process. In this work, we proposed a facile method to reduce the dark current of Cu2O/Au Schottky PDs, and further demonstrated its application in high SNR imaging system. By applying a small external bias of -120 mu V, the dark current of PDs decreases from 27 nA to 0.6 nA, with 4023% improvements of ON/OFF ratio. Additonaly, a model based on free carriers generated by rich trap-state and thermal excitation under asymmetric internal electric field was proposed to understand this phenomenon. Finally, a high-resolution image with high SNR (48 dB) was acquired, which is close to that of commercial Si-CDD and CMOS. Our results provide a convenient way to reduce the dark current and improve the image quality, also suggest Cu2O is potentially an attractive candidate to be applied in optical imaging applications.