Exposing Digital Forgeries Through Specular Highlights on the Eye
When creating a digital composite of two people, it is difficult to exactly match the lighting conditions under which each individual was originally photographed. In many situations, the light source in a scene gives rise to a specular highlight on the ey
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Abstract. When creating a digital composite of two people, it is difficult to exactly match the lighting conditions under which each individual was originally photographed. In many situations, the light source in a scene gives rise to a specular highlight on the eyes. We show how the direction to a light source can be estimated from this highlight. Inconsistencies in lighting across an image are then used to reveal traces of digital tampering. Keywords: Digital Tampering, Digital Forensics.
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Introduction
The photograph in Fig. 1 of the host and judges for the popular television show American Idol was scheduled for publication when it caught the attention of a photo-editor. Coming on the heels of several scandals that rocked major news organizations, the photo-editor was concerned that the image had been doctored. There was good reason to worry – the image was a composite of several photographs. Shown in Fig. 1 are magnifications of the host’s and judge’s eyes. The inconsistencies in the shape and position of the specular highlight on the eyes suggest that the people were originally photographed under different lighting conditions. In this work, we show how the location of a specular highlight can be used to determine the direction to the light source. Inconsistencies in the estimates from different eyes, as well as differences in the shape and color of the highlights, can be used to reveal traces of digital tampering. In related work, the authors of [5] showed how to estimate the light source direction in 2-D. While this approach has the benefit of being applicable to arbitrary objects, it has the drawback that it can only determine the direction to the light source within one degree of ambiguity. In contrast, we estimate the full 3-D light source direction by leveraging a 3-D model of the human eye. Although not specifically developed for a forensic setting, the authors of [7] described a technique for computing an environment map from eyes that embodies the illumination in the scene. While the environment map provides a rich source of information about the lighting, it has the drawback of requiring a relatively high-resolution image of the eye. T. Furon et al. (Eds.): IH 2007, LNCS 4567, pp. 311–325, 2007. c Springer-Verlag Berlin Heidelberg 2007
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M.K. Johnson and H. Farid
Fig. 1. This photograph of the American Idol host and judges is a digital composite of multiple photographs. The inconsistencies in the shape and position of the specular highlight on the eyes suggest that these people were originally photographed under different lighting conditions. Photo courtesy of Fox News and the Associated Press.
We describe how to estimate the 3-D direction to a light source from specular highlights on the eyes. We show the efficacy of this approach on synthetic and real images and visually plausible forgeries.
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Methods
The position of a specular highlight is determined by the relative positions of the light source, the reflective surface and the viewer (or camera). In Fig. 2, for example, is a diagram showing the cr
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