Reliable Camera Model Identification Using Sparse Gaussian Processes

Identifying the model of a camera that has captured an image can be an important task in criminal investigations. Many methods assume that the image under analysis originates from a given set of known camera models. In practice, however, a photo can come from an unknown camera model, or its appearance could have been altered by unknown post-processing. In such a case, forensic detectors are prone to fail silently. One way to mitigate silent failures is to use a rejection mechanism for unknown examples. In this work, we propose Gaussian processes (GPs), which intrinsically provide such a rejection mechanism. This makes GPs a potentially powerful tool in multimedia forensics, where forensic analysts regularly work on images from unknown origins. We demonstrate that GPs scale well to the task of camera model identification. Probabilistic predictions from a GP classifier achieve high classification accuracy for known camera models while providing reliable uncertainty estimates. The built-in uncertainty estimates effectively tackle open-set camera model identification, outperforming two state-of-the-art methods.