Submitted by admini on Fri, 2012-01-27 07:57
Image Forensics
A digital photo is a representation of a discrete mathematical function having a finite set of digital values called pixels. When commiting image forgery, the photo is opened in an image editing software (e.g., Adobe Photoshop) and modifications are carried out. These modifications change the algebraic and statistical properties of the image. What is important is that always they leave behind some detectable traces.
To determine whether a photo is original (not modified), our system analyzes it using a number of separate automatic methods. Here is a brief description of the core parts of the system. However sophisticated these core parts may be, we always provide the user with a simple to use report with clearly identified suspects.
- Digital imaging device validation. Digital images created by various imaging devices have different properties. Using millions of digital images, we modeled almost all existing cameras and created a unique database, which can effectively determine about the origin of the analyzed photo. The database is continuously updated with new models of devices.
- Traces of photo-editing software. Image manipulations are carried out using a photo-editing software. Many of software products use specific quantization tables for creating JPEG files. We collected an extensive database allowing us to compare the quantization tables used in the analyzed image and quantization tables of existing photo software products.
- Detecting cloning. Cloning is a very commonly used way of digital image forgery creation. In this instance, a part of the image is copied and pasted into another part of the same image, with the intention to hide an object or a region of the image.
- Multiple JPEG detection. The JPEG file format is the most widely used image format. When altering a JPEG image, it is loaded into a photo-editing software and after manipulations are carried out, the image is re-saved (compressed again). The re-saving operation introduces specific detectable changes into the image.
- Analysis of Exif: Exchangeable image file format (Exif) is the specification of the image file format. Exif contains a number of metadata tags containing data about the image. Finding an inconsistency or traces of software in Exif signifies photo modification. Since Exif data are text data and are simply editable, it is very easy to keep them consistent. Thus, an analysis of Exif is an insufficient way for detecting image forgery. Furthermore, many photo editing software do not change the Exif data at all and keep them consistent.
- We have developed further methods for detecting the traces of cropping, JPEG blockiness inconsistencies, resizing and rotation, light condition inconsistencies, noise inconsistencies and others for specific purposes.
The danger of Photoshop (source: YouTube) On YouTube we can find a number of tutorials how to make insurance frauds using photo editors.
