With the power of Photoshop and other photo manipulating software, it’s not hard to create a convincing fake image. This can be good in terms of art and creative outlets where image manipulation can serve to break through many limitations. However, it can also produce false evidence in courts and generate misinformation through the media. Hence, the field of photo forensics has been developed to dispel these fake images. In this video, you will see how these photos can be determined as fake by finding inconsistencies in the shadows of the image:
Though the math and process sounds very complicated, the idea is rather simple. If there is one strong light source, all the shadows in the image must fall correspondingly to that light source. A straight line must be able to travel from a point on the shadow, to a point on the object creating the shadow, to the light source itself (Via Mashable). Though objects and shadows can be somewhat ambiguous, forensic analysts can still project conservative estimates of where the light source may be. By comparing multiple points of estimated projections, inconsistencies can be determined. The more points that are added, the higher the probability is of determining whether a photo is real or fake.
“It’s well known that observers have difficultly judging the physical consistency of shadows. So we allow the observer to do what the computer finds challenging which is understand the scene content, and we let the computer do what the observer finds difficult which is to assess the validity of any geometric constraints.”
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