When we tested the fifth image, the similarity value we obtained was close to zero. Given they're correlated, we can say the images likely came from the same camera. When we compared four of the five image fingerprints, we obtained values well above 2,000. We extracted a unique fingerprint from each image using signal processing filters and compared how similar they were to each another.Ī high value indicates they are very similar and probably correlated, while a low value indicates that they are dissimilar and unlikely to be correlated. This was verified using sensor pattern noise and statistical methods. We inspected the images using Phil Harvey's ExifTool and were able to determine that four images were taken by one camera, with the remainder taken by another. The Byethorne duck was photographed with a knife embedded in its head. Here we'll be focusing on the metadata captured in images (level 5 in the schema above). It is often the unseen that begins our investigation rather than the seen. 6.Pixel: scaling, cropping, cloned or resaving.5.File format: metadata, file compression, thumbnails and markers.4.Image Sensor: fixed pattern noise and colour filter defects.3.Optical: lens distortion or aberrations.2.Geometry: vanishing points, distances within the image and 3D models.1.Physics: shadows, lighting and reflections.This pipeline is often broken down into six key areas: Images cannot always be trusted as an accurate depiction of what occurred.įor example, I recently analysed several photos for the RSPCA showing a duck with a knife embedded in its head to determine if they were photoshopped.Īuthorities are increasingly asking images to be verified by forensic experts, but how is this done and where is it headed? The image pipelineĪnalysts currently rely on knowledge of the "image pipeline" to inspect and validate images. While this may be convenient for your Instagram feed, it presents a unique challenge for law enforcement. For as long as humans have been making images, we have also been manipulating them.Ĭomplex darkroom techniques were once required to modify images but now anyone with a smartphone can apply hundreds of changes using freely available tools.
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