Localisation of image tampering

Abstract

A method and device (8) for verifying the authenticity of media content is provided. According to an embodiment accurate tampering location for digital image authentication is provided. Typically, a suspect image is divided into blocks. For each block, an authentication bit is generated by computing a property of the image content and then thresholding said property to give a '0' or '1'. The authentication bits of the suspect image are compared with those of the original image. If there is a mismatch, and the content has indeed been tampered, tampering is detected. A mismatch due to allowable operations, such as e.g. compression, is called a false alarm, which should be avoided. A so-called ROC curve (Receiver Operating Characteristic) gives the relation between detection probability and false alarm probability. Preferably, the threshold used to determine the authentication bits represents an operation point on the ROC curve. In accordance with an embodiment of the invention, an operation point corresponding to a low false alarm probability is initially chosen. In order to more precisely identify a tampered image area, the authentication decisions are repeated for neighbouring blocks, using a different operation point. This continues until no further tampered blocks are found. Thus improved tampering localisation is provided, being valuable e.g. to authenticate images captured by e.g. a security camera, and localise any tampered areas, whereby the value of these images is increased as e.g. evidence in a court of law.

Description

technical field [0001] The present invention is generally in the field of digital imaging, and in particular relates to the authentication of digital images and videos, and more particularly to the identification and location of image tampering for authentication purposes. Background technique [0002] The need to easily edit and alter images and video in digital form has fueled the need for devices that can authenticate original, unaltered content. When it is judged that an image has been changed, it is also desirable to have a flag indicating that the image area has been changed. [0003] The authentication problem is complicated by the fact that some image changes are acceptable, such as those due to attenuated compression. These changes may cause a slight degradation in image quality but do not affect the interpretation or intended use of the image. The result is that traditional authentication techniques using cryptography are no longer suitable, as these methods typi...

AI Technical Summary

Problems solved by technology

[0003] The identification problem is complicated by the fact that some image changes are acceptable, such as those due to decaying compression

These changes may cause a slight degradation in image quality but will not affect the interpretation or intended use of the image

As a result, traditional authentication techniques using cryptography are no longer suitable, as these methods typically only account for changes of only one bit of the image when tampering occurs

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