At the time of initial recording, most cameras generate a thumbnail sized version of the full resolution image. Thumbnails are themselves stored as a JPEG image and embedded within the header of the full resolution image. A thumbnail is used to preview the image thus avoiding having to load and display the full resolution image. The process by which a thumbnail is created and stored is somewhat distinct across different camera manufacturers and photo editing software. As a result, the image thumbnail, an often over-looked part of a digital image, can be useful in an image forensic setting.
Welcome to the Fourandsix blog, where you’ll find tips on image forensics techniques and commentary on issues relevant to photo tampering and the responsible use of imaging tools.
Over the years I have worked on several scientific misconduct cases and have been surprised at the egregiousness and scope of the misconduct. From the biological to the astronomical, many scientific disciplines now rely on some form of scientific imaging. As a result, conclusions in scientific studies often rely on interpreting data in digital images. Because scientific images tend to be simpler than photographs of scenes and people, it is often much easier to manipulate them and can be much harder to detect the manipulations.
Adobe has released a free, public beta of its just-announced Photoshop CS6 version, and lots of users are busy absorbing the substantial list of new features. I thought I’d take a look at some of these new features from the standpoint of a truthful photo editing workflow, and one feature that jumped out at me is the new Adaptive Wide Angle filter. It’s an extremely clever and useful piece of technology, but it also reveals the slippery slope that accompanies many attempts to define what is “truth” in a photo and what tools should be allowed when a strict adherence to truth is required.
Printed and scanned documents are routinely used in civil and criminal cases, for e-commerce, and to prove provenance of historic and valuable artifacts. Text-based documents in particular, can be relatively easy to alter by digitally inserting or removing a signature, text, or a date. Printed text contains imperfections that are distinct and depend on the type of printer, the printer manufacturer, the age of the printer, and the printer’s toner level. These distinct printer imperfections can be quantified and measured. Deviations in these imperfections within a document can then be used as evidence of a fraud.
Predators (lions, wolves, humans) typically have two forward facing eyes, while prey (gazelles, rabbits, chicken) typically have two eyes on either side of their head. The eyes of animals that are preyed upon are ideally positioned to allow them to see in front of and behind them and therefore detect danger from any direction. The eyes of animals that hunt are ideally positioned to allow them to triangulate the 3-D location of their prey, even it if means that they have a narrower field of view. The same mechanisms that allows animals to efficiently hunt (stereopsis) underlies how 3-D information can be extracted from a pair of images.