The ever-increasing use of synthetically generated content in different sectors of our everyday life, one for all media information, poses a strong need for deepfake detection tools in order to avoid the proliferation of altered messages. The process to identify manipulated content, in particular images and videos, is basically performed by looking for the presence of some inconsistencies and/or anomalies specifically due to the fake generation process. Different techniques exist in the scientific literature that exploit diverse ad-hoc features in order to highlight possible modifications. In this paper, we propose to investigate how deepfake creation can impact on the characteristics that the whole scene had at the time of the acquisition. In particular, when an image (video) is captured the overall geometry of the scene (e.g. surfaces) and the acquisition process (e.g. illumination) determine a univocal environment that is directly represented by the image pixel values; all these intrinsic relations are possibly changed by the deepfake generation process. By resorting to the analysis of the characteristics of the surfaces depicted in the image it is possible to obtain a descriptor usable to train a CNN for deepfake detection: we refer to such an approach as SurFake. Experimental results carried out on the FF++ dataset for different kinds of deepfake forgeries and diverse deep learning models confirm that such a feature can be adopted to discriminate between pristine and altered images; furthermore, experiments witness that it can also be combined with visual data to provide a certain improvement in terms of detection accuracy.

翻译：日常生活中各领域（尤其是媒体信息）中合成内容的日益普及，强烈需要深度伪造检测工具以避免虚假信息的扩散。识别被篡改内容（尤其是图像和视频）的过程，主要通过寻找因伪造生成过程导致的某些不一致性和/或异常现象来实现。现有科学文献中存在多种利用特定特征来突显可能修改的技术。本文旨在探究深度伪造生成如何影响场景在采集时的整体特征。具体而言，当图像（视频）被捕获时，场景的全局几何特性（如表面）和采集过程（如光照）决定了唯一的环境，该环境直接由图像像素值表征；深度伪造生成过程可能改变所有这些内在关系。通过分析图像中描绘表面的特征，可获取可用于训练CNN进行深度伪造检测的描述符：我们将此方法称为SurFake。在FF++数据集上针对不同类型深度伪造篡改和多种深度学习模型进行的实验结果表明，该特征可有效区分原始图像与篡改图像；此外，实验还证明该特征可与视觉数据结合使用，从而在检测精度方面提供一定改善。