DEEP LEARNING FOR FORENSICS

The advent of media sharing platforms and the easy availability of advanced photo or video editing software have resulted in a large quantity of manipulated images and videos being shared on the internet. While the intent behind such manipulations varies widely, concerns on the spread of fake news and misinformation is growing. Therefore, detecting manipulation has become an emerging necessity. Different from traditional classification, semantic object detection or segmentation, manipulation detection/classification pays more attention to low-level tampering artifacts than to semantic content. The main challenges in this problem include (a) investigating features to reveal tampering artifacts, (b) developing generic models which are robust to a large scale of post-processing methods, (c) applying algorithms to higher resolution in real scenarios and (d) handling the new emerging manipulation techniques. In this dissertation, we propose approaches to tackling these challenges. Manipulation detection utilizes both low-level tamper artifacts and semantic contents, suggesting that richer features needed to be harnessed to reveal more evidence. To learn rich features, we propose a two-stream Faster R-CNN network and train it end-to-end to detect the tampered regions given a manipulated image. Experiments on four standard image manipulation datasets demonstrate that our two-stream framework outperforms each individual stream, and also achieves state-of-the-art performance compared to alternative methods with robustness to resizing and compression. Additionally, to extend manipulation detection from image to video, we introduce VIDNet, Video Inpainting Detection Network, which contains an encoder-decoder architecture with a quad-directional local attention module. To reveal artifacts encoded in compression, VIDNet additionally takes in Error Level Analysis (ELA) frames to augment RGB frames, producing multimodal features at different levels with an encoder. Besides, to improve the generalization of manipulation detection model, we introduce a manipulated image generation process that creates true positives using currently available datasets. Drawing from traditional work on image blending, we propose a novel generator for creating such examples. In addition, we also propose to further create examples that force the algorithm to focus on boundary artifacts during training. Extensive experimental results validate our proposal. Furthermore, to apply deep learning models to high resolution scenarios efficiently, we treat the problem as a mask refinement given a coarse low resolution prediction. We propose to convert the regions of interest into strip images and compute a boundary prediction in the strip domain. Extensive experiments on both the public and a newly created high resolution dataset strongly validate our approach. Finally, to handle new emerging manipulation techniques while preserving performance on learned manipulation, we investigate incremental learning. We propose a multi-model and multi-level knowledge distillation strategy to preserve performance on old categories while training on new categories. Experiments on standard incremental learning benchmarks show that our method improves the overall performance over standard distillation techniques