Tag, evidence
15.10.–15.12.2015
5. Photo Forensics: Can You Enhance That?

When you view a sign from a highly oblique angle, the perspective distortion may cause the text and graphics to be unrecognizable. To make the sign interpretable, you could change your vantage point and view the sign head-on. But what if the sign appears at an oblique angle in a photograph? Is it possible to remove the perspective distortion and view the sign head-on? This question arises in forensic settings when the evidence contained within an image is obscured by perspective distortion. In this post, I describe how perspective distortion can be removed to reveal, for example, the identity of a barely visible license plate. more

Published: 15.12.2015
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2. Photo Forensics: In the Shadows

When asked to judge the location of the sun relative to this scene, most people would respond quickly that it is on the right. When asked to localize the sun more precisely, most people would need to think before responding and they would still be inaccurate. (For evidence of this perceptual failure see 1Hany Farid and Mary J. Bravo. Image Forensic Analyses that Elude the Human Visual System. SPIE Symposium on Electronic Imaging, San Jose, CA, 2010., but also test yourself: the answer is below.) The difficulty we have localizing light sources is surprising because the scene contains abundant information for making this judgment. The fact that we cannot easily perceive information that is clearly contained within the image provides an opening for forensic analysis because forgers may be unaware that they have introduced telltale clues that we can easily detect. In this post, we will see how to determine whether the cast shadows in an image are consistent with a single light source. If the shadows are inconsistent in a scene that is clearly illuminated by a single source (e.g., the sun), then we have strong evidence of image tampering. more

Published: 29.10.2015
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5. Popular, not Populist

My apologies for the extended silence. I have been putting the finishing touches to a book about the relation between popular culture, art and photography, which will also be the subject of this blog entry.

It seems generally accepted now that photography became a modern medium of art in the 1920s. This was when it gave up its resistance to the widespread industrial basis of photography (Pictorialism is thought to have typified that resistance) and came into a close or parallel relation to the medium’s various social functions. Photography triumphed artistically by remaking, diverting, re-presenting or otherwise contemplating its ‘applied’ forms such as the document, the film still, the advertisement, the commercial portrait and the archival image. more

Published: 27.05.2013
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