Learning Unified Deep-Features for Multiple Forensic Tasks

Recently, deep learning researchers have developed a technique known as deep features in which feature extractors for a task are learned by a CNN. These features are then provided to another classifier, or even used to perform a different classification task. Research in deep learning suggests that in some cases, deep features generalize to seemingly unrelated tasks. In this paper, we develop techniques for learning deep features that can be used across multiple forensic tasks, namely image manipulation detection and camera model identification. To do this, we develop two approaches for building deep forensic features: a transfer learning approach and a multitask learning approach. We experimentally evaluate the performance of both approaches in several scenarios and find that: 1) features learned for camera model identification generalize well to manipulation detection tasks but manipulation detection features do not generalize well to camera model identification, suggesting a task asymmetry, 2) deeper features are more task specific while shallower features generalize well across tasks, suggesting a feature hierarchy, and 3) a single, unified feature extractor can be learned that is highly discriminative for multiple forensic tasks. Furthermore, we find that when there is limited training data, a unified feature extractor can significantly outperform a targeted CNN.