**1.2.2 Digital watermarking as a technique for digital media data identification**

The most known decision for maintenance of such protection, in particular the rights to the media information presented in a digital form, is application of digital watermarks (DW). Robust DW represent some information which is built in readout of a signal marked by them. DW, as a rule, contain some authentic code, the information on the proprietor or the operating information for reproduction and copying tools. Unlike usual watermarks, DW can be not only visible, but also (as a rule) invisible because by the nature DW are distortions of a signal, which is intended for perception by the person in the first place, and, hence, for preservation of consumer qualities of protected audiovisual production should be as less as possible. Invisible DW are analyzed by the special decoder which renders the decision on their presence, and if necessary, extracts the hidden message. The most suitable objects of protection by means of DW are static images, files of audio- and the video data[1- 3]. DW applications are not limited to information security applications. The basis areas of DW technology can be united in four groups:


300 Applications of Digital Signal Processing

Widening of digital audio and videorecording devices distribution and an abrupt increase of storage density had led to situation where the most frequently identification case is identifiable records that are external to identifiable device, leading to complete absence of the primary physical state of the primary "source" and file system properties. Than the rest identification way are the identification based on file format features and identification

Copyright protection task operates with the same features, but the signal can be presented after multiple format conversions, which preserve consumption quality but changes the physical representation of original signal, so the identifiable and applicable features are ones

Currently questions of identification of analog audio, still images and video recording devices are well researched and are based on traces which the recording device leaves on the carrier in process of writing at change of its physical properties. It is widely used at any carrying out of the expertizes which example is, in particular, phototechnical examination. Phototechnical expert appraisal represents judicial expertize on research of facsimiles of various property and the content, photos (including numeral), paper pictures (photo), for definite purposes of criminal, civil or arbitration legal proceedings. Each picture contains information about the circumstances concerning procedure of manufacturing. Phototechnical expert appraisal is produced with a view of identification of objects by their images photos, photographic materials and laboratory accessories on traces on negatives and positives, ascertainment of type and mark of "unknown" photofilms, detections on photos traces of tampering , ascertainment of other circumstances linked to photographing




The immediate practical task of identification of records can be put in various variants. In practice of ascertainment and protection of copyrights, and also detections of a source of media object the most often situations are when record on the initial carrier is exposed to identification - ascertainment or a refutation of the fact of an origin of record from the presented device is required, or the record copied on other carrier (possibly with automatic format conversion, compression of dynamic range or other variants of postprocessing) is exposed to identification. In the latter case initial record obtaining, as a rule is complicated, and frequently impossible. It is required to determine a record ownership to the device

based on features of recording path and postprocessing.

containing in digital *content* rather than *format* representation.

and handling of photographic materials (photos, photographic paper).

a method of detection its manufacturer, original form recovery.

presented by means of another records set certainly acquired with it.

**1.2.2 Digital watermarking as a technique for digital media data identification** 

The most known decision for maintenance of such protection, in particular the rights to the media information presented in a digital form, is application of digital watermarks (DW). Robust DW represent some information which is built in readout of a signal marked by

Thus, phototechnical expert appraisal tasks are subdivided on:

according to existing classification;

**1.2.1 Practical tasks of identification** 

film);


Definition of the received information authenticity, plays a special role in a modern information exchange. Usually the digital signature is used for authentication. However it is not quite appropriate for authentication of multimedia information. The message with attached digital signature should be stored and transferred absolutely precisely, «bit-to-bit», while multimedia information can slightly be changed both at storage (at the expense of compression and due to insufficient correcting ability of a code), and at transfer (influence of single or package errors in a communication channel). Thus its quality remains admissible for the user, but the digital signature will not work, so the addressee cannot distinguish true, though and a little changed message from the completely false one. Besides, the multimedia data can be transformed from one format to another, thus traditional means of definition of integrity also will not work.

It is possible to tell that DW are capable to protect the content of digital audio/video, instead of its digital representation in the form of sequence of bits. An essential lack of the digital signature is also that it is easy to completely remove it from the message and attach the new signature. Signature removal will allow the infringer to refuse authorship or to mislead the lawful addressee concerning authorship of the message. Modern systems of DW are projected so that to minimise possibility of similar infringements without simultaneous essential deterioration of record. DW should be robust or fragile (depending on application) to deliberate and casual influences. If DW is used for authenticity acknowledgement, inadmissible change of the container should lead to DW destruction (fragile DW). If DW contains an identification code, a firm logo, etc. it should remain at the maximum distortions of the container, of course, not leading to essential distortions of an initial signal. Thus, at use DW the basic problem are the attacks, which aim is infringement of their integrity. It is possible to distinguish the following attacks: the attacks directed on DW removal, the geometrical attacks directed on distortion of the container, cryptographic attacks, attacks against the used embedding method and DW checking procedure [4-6]. Researching new methods of embedding DW, robust against malicious attacks is base problem in researching new methods of protection of the multimedia information presented in a digital form.

Along with clear advantages of a digital watermarks embedding, its application demands inclusion of the additional block of embedding in structure of each recording device. For already existing modern mobile digital recording devices it leads to at least updating of the microprogram and it can be impossible if computing resources of the device are limited.

Digital Camera Identification Based on Original Images 303

1. A basis of camera-by-image identification is the analysis of features leaved to area of

2. As an input image format for creation of image identifying the camera, and subsequent identification of belonging the arbitrary checked image to the camera, the most suitable is the raster format without any compression. In view of that similar formats of representation are last formats at logical level for the majority of visual information output devices. It is possible to convert any format of digital images without quality

Thus, for digital photocameras it is possible to select two classes of features which could be

1. Hardware features are reflections of deviations of characteristics of a sensor control steady in time and the subsequent units of handling, including ADC, as separate device in the received digital image. Generally sensor control signs allow to identify a specific copy of the device. In particular for digital cameras those are defects and deviations within tolerances of separate photosensitive elements, defects of elements of the unit of

2. Features of postprocessing algorithms. The digital image received at output of ADC of digital cameras is then further processed. In digital cameras algorithms of the postprocessing that make the greatest impact on the resulted image are algorithms of image recovery from a mosaic (Bayer) structure of a sensor [17], algorithms of increasing contour sharpness and noise reduction. In the majority of the most widespread photocameras of the lower price segment algorithms of postprocessing can not be switched off and the only image formats accessible outside the camera are JPEG

In view of that algorithms of postprocessing are the general sometimes for all models of one vendor [16, 23], for detection by sample-unique features it is necessary to take identification

Let's consider used algorithmic primitives of interpolation the colors applied to form the

r(1,1) g(1,2) r(1,3) g(1,4) r(1,5) g(1,6) … g(2,1) b(2,2) g(2,3) b(2,4) g(2,5) b(2,6) … r(3,1) g(3,2) r(3,3) g(3,4) r(3,5) g(3,6) … g(4,1) b(4,2) g(4,3) b(4,4) g(4,5) b(4,6) … r(5,1) g(5,2) r(5,3) g(5,4) r(5,5) g(5,6) … g(6,1) b(6,2) g(6,3) b(6,4) g(6,5) b(6,6) … … … … … … … …

Let light filters of primary colors are allocated in Bayer's grid according to a picture 1. The algorithms used for recovery of missing color components, are represent "know-how" of vendors and, as a rule, vary depending on model of the camera and type of a photosensitive matrix. However most often they are constructed on the basis of linear and median

on parameters of an analog section, i.e. on the first class of features.

filtrations primitives, threshold gradients and persistence of color tone.

**1.4 Methods of matrix data-to-image conversion** 

color image in digital photographic cameras.

Fig. 1. Color filter array in the Bayer structure

pixels of the given image.

used as a basis for identification:

or processed TIFF.

a photosensitive matrix [16, 20].

loss.

Besides it, embedding worsens consumer characteristics of received record that is not always tolerable, and, at special importance of originality of digital record, can be inadmissible.

Other way of authenticity ascertainment is identification on the basis of recording path features, which are presented in a digital record.
