Source smartphone identification for digital zoomed images

Sensor noise caused by photo response non-uniformity (PRNU) has been widely accepted as a reliable fingerprint for source camera identification (SCI). In the sensor based camera identification methods, the extracted noise from a test image needs to be absolutely synchronized with the camera fingerprint. However, for the images captured under digital zoom, this requirement is not satisfied, which is very common for smartphone shooting environment due to no optical zoom available. Here, through carefully studying about the effect of the digital zoom on the sensor-based SCI, we found several characteristics in this case, and proposed a novel metric to enhance the SCI performance for images taken with digital zoom. Experimental results show that the proposed metric outperforms the benchmark metric for source smartphone identification on digital zoomed images by evaluating the ROC performance.