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The camera never lies
The camera never lies
Is it real
Is it real
Spot the forgery
Spot the forgery
Spot the forgery
Spot the forgery
Spot the forgery
Spot the forgery
Spot the forgery
Spot the forgery
Spot the forgery
Spot the forgery
Spot the forgery
Spot the forgery
More like this
More like this
Protection of Children Act 1978 Counter-Terrorism Act 2008 Section 58
Protection of Children Act 1978 Counter-Terrorism Act 2008 Section 58
Exchangeable image format (Exif) data provides a wealth of information
Exchangeable image format (Exif) data provides a wealth of information
Some forensic methods
Some forensic methods
Build a fingerprint for suspected source camera
Build a fingerprint for suspected source camera
Sensor fingerprinting
Sensor fingerprinting
Photo response non-uniformity (PRNU)
Photo response non-uniformity (PRNU)
Denoising filter specification
Denoising filter specification
Latent/exemplar fingerprint matching
Latent/exemplar fingerprint matching
Digital image analysis and evaluation (DIANE) MATLAB code
Digital image analysis and evaluation (DIANE) MATLAB code
Source camera identification
Source camera identification
Robustness of PRNU method (application to social networking)
Robustness of PRNU method (application to social networking)
Forgery detection using PRNU
Forgery detection using PRNU
Forgery detection using PRNU
Forgery detection using PRNU
Some forensic methods
Some forensic methods
JPEG Compression scheme
JPEG Compression scheme
JPEG File Headers
JPEG File Headers
JPEG File Headers
JPEG File Headers
Analysis of DCT coefficients
Analysis of DCT coefficients
Analysis of DCT coefficients
Analysis of DCT coefficients
Analysis of DCT coefficients
Analysis of DCT coefficients
Analysis of DCT coefficients
Analysis of DCT coefficients
Resources
Resources
Contact
Contact

Презентация: «The camera never lies». Автор: admin. Файл: «The camera never lies.ppt». Размер zip-архива: 3970 КБ.

The camera never lies

содержание презентации «The camera never lies.ppt»
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1 The camera never lies

The camera never lies

Advances in digital image forensics

Wordle [word cloud] containing titles of image forensics publications 2010-12 [http://www.cs.dartmouth.edu/~farid/dfd/index.php/publications]

Dr Stuart Gibson (s.j.gibson@kent.ac.uk) School of Physical Sciences, University of Kent

2 Is it real

Is it real

Which camera?

Objective for image forensics

Image integrity check

Source camera identification

Hurricane Sandy image forgery

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3 Spot the forgery

Spot the forgery

The August 2007 cover of the scientific publication Nature featured three autonomous aircraft taking atmospheric measurements. The top and bottom aircrafts, however, were cloned copies of each other. After a keen-eyed reader discovered this photo alteration, the Editors printed the following clarification: “The cover caption should have made it clear that this was a montage. Apologies.”

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4 Spot the forgery

Spot the forgery

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5 Spot the forgery

Spot the forgery

A political ad for George W. Bush, as he was running for President, shows a sea of soldiers as a back drop to a child holding a flag. The original image included Bush standing at a podium, but he was removed by digitally copying and pasting several soldiers from other parts of the image. After acknowledging that the photo had been doctored, the Bush campaign said that the ad would be re-edited and re-shipped to TV stations.

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6 Spot the forgery

Spot the forgery

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7 Spot the forgery

Spot the forgery

In a doctored photograph, British politicians Ed Matts, conservative candidate for Dorset South, and Ann Widdecombe, conservative candidate for Maidstone and the Weald, are shown holding a pair of signs that together read “controlled immigration — not chaos and inhumanity”. This picture appeared as part of Matts’ election literature. The original photograph, however, shows the same two candidates campaigning for a Malawian family of asylum seekers to be allowed to stay in Britain. Widdecombe said she was “happy to be associated with either message”.

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8 Spot the forgery

Spot the forgery

A Missouri University professor and co-authors retracted their paper (Cdx2 Gene Expression and Trophectoderm Lineage Specification in Mouse Embryos) published in Science after an investigation revealed that accompanying images were doctored. Contrary to conventional wisdom, the published research presented evidence that the first two cells of mouse embryos possess markers that indicate from a very early stage whether they will grow into a fetus or placenta. An investigating university committee found that lead author and post-doctoral researcher deliberately altered images of the embryos.

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9 More like this

More like this

http://www.fourandsix.com/photo-tampering-history/tag/science

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10 Protection of Children Act 1978 Counter-Terrorism Act 2008 Section 58

Protection of Children Act 1978 Counter-Terrorism Act 2008 Section 58

of the Terrorism Act 2000 Copyright law

Digital images and the law

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11 Exchangeable image format (Exif) data provides a wealth of information

Exchangeable image format (Exif) data provides a wealth of information

including camera make and model. But can we trust Exif data? [PhotoMe demo here]

Properties of a digital image

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12 Some forensic methods

Some forensic methods

Majority of methods enable camera classification. Photo response non-uniformity can differentiate between images taken from two cameras of same make and model.

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13 Build a fingerprint for suspected source camera

Build a fingerprint for suspected source camera

To obtain the fingerprint for a specific device: Take at least 50 natural scene images using suspected source camera. Individually filter each image using a wavelet denoising filter. Average together the filtered images to produce unique fingerprint for camera. The averaging process removes the majority of random noise leaving you with the stochastic fingerprint particular to the camera of interest Some artefacts remain but these diminish when more images are used (~ 300 Recommended by Fridrich)

14 Sensor fingerprinting

Sensor fingerprinting

‘Exemplar’ fingerprint:- known to have originated from a specific source camera. ‘Latent’ fingerprint:- lifted from an evidential image.

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15 Photo response non-uniformity (PRNU)

Photo response non-uniformity (PRNU)

Image degradation model

Noise residual

true scene

observed image

denoised image

random additive noise component

consistent between images

Estimate of exemplar fingerprint given by mean noise residual

Lukas, Fridrich & Goljan | In SPIE Electonic Engineering | 2005 | 249-260

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16 Denoising filter specification

Denoising filter specification

Daubechies db8 wavelet. Filter detail coeffs for first 4 levels of decomposition. ML estimate of variance based on local neighbourhood.

Mihcak, Kozintsev, Ramchandran, Moulin | IEEE Trans Sig Proc |1999 | 6(12) | 300-303

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17 Latent/exemplar fingerprint matching

Latent/exemplar fingerprint matching

Obtain the exemplar (device) fingerprint of the camera (s) of interest. Obtain the exemplar of a number of other cameras (1, 2, 3...) Filter evidential images with wavelet denoising filter. Correlate latent print with exemplar fingerprints of all cameras. High correlation coefficient obtained if the fingerprints match.

Determine correlation coefficient between noise pattern and fingerprints for cameras including suspected source

Camera 1 fingerprint

Camera 2 fingerprint

Image noise pattern (latent fingerprint)

Evidential image

Camera 3 fingerprint

......

Apply filter

Camera s fingerprint

18 Digital image analysis and evaluation (DIANE) MATLAB code

Digital image analysis and evaluation (DIANE) MATLAB code

Number of images used in estimation of exemplar fingerprint [512x512 image regions, green colour plane]

H0: (Non-matching image)

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19 Source camera identification

Source camera identification

Correlation coefficients for 50 evidential images from a Canon 450D with 8 different cameras including the source.

Image by Welford and Gibson, SPS, UoK

20 Robustness of PRNU method (application to social networking)

Robustness of PRNU method (application to social networking)

Facebook: – Lo-resolution upload and download from iPhone 4S [720x960]

Facebook : Hi-resolution upload and download from iPhone 4S [1536x2048]

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21 Forgery detection using PRNU

Forgery detection using PRNU

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Cyber Security Seminar

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22 Forgery detection using PRNU

Forgery detection using PRNU

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23 Some forensic methods

Some forensic methods

Methods based on JPEG artefacts and decompression information are particularly popular in the research literature [see word cloud]

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24 JPEG Compression scheme

JPEG Compression scheme

For the lossy JPEG compression method the input image (a) is separated into 8x8 image blocks in a pre-processing step. The DCT of each image block is calculated separately (b). The significant coefficients of the DCT are usually located in the top left hand corner (c) and are attributable to low spatial frequencies in the input image.

Dr. Stuart Gibson, SPS

PS507: Unit 2 – Digital Image Processing

25 JPEG File Headers

JPEG File Headers

Discrete Quantisation Table (DQT) Required for decompression. Optimised for hardware and intended use of camera.

DQT for Canon EOS40D

DQT for iPhone 3G

Dr. Stuart Gibson, SPS

26 JPEG File Headers

JPEG File Headers

Forensic value of DQT Indicator of make and model. All JPEG files headers have one (even when Exif metadata has been deliberately removed). DQT may be overwritten when Image tampering has taken place (compare with metadata – if still present). File is transferred – social networking, mobile phone. In some cases primary DQT may be inferred from the histograms of discrete cosine transformation coefficients even if the image has been compressed twice...

Dr. Stuart Gibson, SPS

27 Analysis of DCT coefficients

Analysis of DCT coefficients

If the JPEG quality factor is set to 100 we expect to observe a histogram in which adjacent columns are occupied (see below). This is because all entries in the DQT are 1 and no quantisation of coefficient values takes place.

coefficient histogram for a single spatial frequency

Dr. Stuart Gibson, SPS

PS507: Unit 2 – Digital Image Processing

28 Analysis of DCT coefficients

Analysis of DCT coefficients

Single compression When coefficient magnitudes are quantised by a divisor of say 3, we expect to see every third column occupied. This can be explained by the loss in accuracy due to rounding of values that are not multiples of 3 e.g. Round(5/3)=2 and 3x2=6 not 5 Hence non-zero columns occur at -12, -9, -6, -3, 0, 3, 6, 9, 12 etc

Spacing between columns is regular and equal to 3.

Dr. Stuart Gibson, SPS

PS507: Unit 2 – Digital Image Processing

29 Analysis of DCT coefficients

Analysis of DCT coefficients

Double compression [Case1: entries in primary DQT > in value than entries in secondary DQT] When coefficient magnitudes are quantised by a divisor in the primary DQT of say 3, then quantised by a divisor in the secondary of DQT of say 2 we expect to irregular column spacing. This is an indicator of image tampering – e.g. Photoshop.

After double compression the spacing between columns is irregular and is equal to 3 then 2 in an alternating sequence.

Dr. Stuart Gibson, SPS

PS507: Unit 2 – Digital Image Processing

30 Analysis of DCT coefficients

Analysis of DCT coefficients

Double compression [Case2: entries in primary DQT < than entries in secondary DQT] When coefficient values are quantised by a divisor in the primary DQT of say 2, then quantised by a divisor in the secondary of DQT of say 3 we expect regular column spacing but irregular column heights. The irregularities in column height also indicate that the image has been recompressed.

Note that here some of the blue columns in the histogram (spaced at intervals of 2) are hidden by the red columns.

Dr. Stuart Gibson, SPS

PS507: Unit 2 – Digital Image Processing

31 Resources

Resources

MATLAB Digital Image Analysis and Evaluation (DIANE) Contact s.j.gibson@kent.ac.uk Dresden image database http://forensics.inf.tu-dresden.de/ddimgdb/ Image forensics bibliography http://www.cs.dartmouth.edu/~farid/dfd/index.php/publications Multimedia forensics bibliography http://www.theonlineoasis.co.uk/cl-web/bibliography/main/sort/year.html

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32 Contact

Contact

Dr Stuart Gibson Address: Room 107 , School of Physical Sciences, Ingram Building. Tel: Ext 3271 Email: s.j.gibson@kent.ac.uk Enquiries regarding collaboration are welcome!

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«The camera never lies»
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