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.