The document discusses how digital watermarking and multimedia forensics can help detect lost identities in multimedia work. Digital watermarking involves embedding secret identifying information directly into multimedia content, while multimedia forensics analyzes intrinsic device and process signatures left in content. Both approaches have limitations but can supplement each other, along with proactively registering works, to attribute authorship. The document also introduces the Multimedia Security and Forensics research group at the University of Surrey which investigates these topics.

1. From Digital Watermarking to
Multimedia Forensics:
How can they help to detect lost
identities in multimedia work?
Shujun LI (李树钧)
Senior Lecturer
Department of Computing
University of Surrey
http://www.hooklee.com

2. 2
Outline
- Where is University of Surrey? 
- “Current” “Solution”: Identities as Metadata
- “New” Solutions?
- Active Solution: Digital Watermarking
- Passive Solution: Multimedia Forensics
- Active Solution: Registering Your Work?
- Expertise of Researchers at Surrey Computing
- Questions and Answers

3. 3
Central London  Guildford, Surrey
Highway A3: 33 miles
Fastest train: 33 mins

4. 4
Guildford Station  Surrey Computing
Guildford Railway
Station  Surrey
Computing (by
walk):
17 mins

5. 5
Dept. Computing @ University of Surrey

6. Detecting Lost Identities:
From Digital Watermarking to Multimedia Forensics
Identities in Multimedia Work

7. 7
Current Solution: Identities as Metadata
- Many media formats support metadata (e.g. Exif,
IPTC IIM and XMP) as part of their file headers.

8. 8
Identities as Metadata: Problems
- Location is public  Unauthorised removal
- Content is public  Unauthorised modification

9. 9
Solutions?
- Active Solution: Digital Watermarking
- Making metadata dependent on the content itself and
secret  Change the metadata = Change the content!
- Active = Some information (watermark) needs
embedding into the protected work when/after the
multimedia work is created in an additional process.
- Passive Solution: Multimedia Forensics
- Discovering information which was NOT actively
embedded into the multimedia work.
- Where is the information from? – Left by the capturing
device/creator as part of the natural process.
- Multimedia work  Device  Owner (Author?)

10. 10
Solutions? (continued)
- Active Solution: Register Your Work?
- Register your multimedia work at a trusted center (e.g.
one maintained by the IPO) actively.
- It does not need to be done by the author, but can be
done by the capturing device (when it connects to the
Internet) or some software (when a piece of multimedia
work is uploaded to the Web).
- One does not have to register the whole work, but only
its (cryptographic and/or perceptual) hash value plus
some identification information (e.g. device ID,
username).
- This can supplement the other two solutions.

11. Detecting Lost Identities:
From Digital Watermarking to Multimedia Forensics
Active Solution:
Digital Watermarking

12. 12
What is a digital watermark?
- A digital watermark is a digital artefact embedded into a
cover work which is also a digital artefact.
- It can be a textual message, an image or just a random
number (like an ID) represented as a number of bits.
- The process of embedding a digital watermark is called
digital watermarking.
- It may be visible or invisible. When it is visible, it mimics
watermarks printed on the paper.

13. 13
Identities as watermark
- A typical application of digital watermarking is
copyright protection.
- The watermark is a copyright claim: “All rights reserved
 Shujun Li, University of Surrey 2012”.
- The watermark needs to be secured! – Only the owner
knows the embedding/extraction key.
- The key can be disclosed to settle an ownership dispute.

14. 14
Conflicting objectives
- Fidelity/Imperceptibility = The watermark should not
degrade the perceptual quality to compromise the value of
the protected work.
- Security = Surviving malicious attacks
- Capacity = More information embedded
- Robustness/Fragility = Surviving benign processing
-  It is impossible to have an ideal system!
Robustness /
Fragility
Fidelity /
Imperceptibility
S e c u r i t y
Capacity

15. 15
Security is complicated!
- Watermarked-only attack
- The attacker has a number of watermarked works only.
- Known-watermark/message attack
- The attacker has access to a number of watermarked works and the
watermark(s) embedded in them.
- Known-cover/original attack
- The attacker has access to a number of watermarked works and the
original cover work(s).
- Chosen-cover/original attack
- The attacker can choose the original cover work(s) in which the
watermark(s) is/are embedded.
- Known-detector attack
- The attacker has access to the detector.

16. 16
Security is complicated!
- Unauthorized watermark embedding
- The attacker wants to forge a watermark or modify a watermark
already embedded.
- Example: to claim the ownership over a work of others.
- Unauthorized watermark removal
- The attacker wants to remove the watermark embedded in a
watermarked work.
- Example: to remove the watermark/fingerprint in a watermarked
(copyrighted) work.
- Unauthorized watermark detection
- The attacker wants to detect the watermark embedded in a
watermarked work.
- Example: to disclose the author of a watermarked work.

17. 17
Watermarking by cameras
- Digital cameras capable of embedding digital
watermarks do (or did?) exist.
- Epson PhotoPC 3000Z/700/750Z/800/800Z
- Kodak DC200/DC260/DC290

18. 18
Watermarking by cameras
- Paul Blythe and Jessica Fridrich, “Secure Digital
Camera,” in Proceedings of 4th Annual Digital
Forensic Research Workshop (DFRWS 2004),
Baltimore, August 11-13, 2004
- Watermark = Biometric (iris) patterns of the
photographer + Cryptographic hash of the image +
Time, Date + …
- The watermarking process is LOSSLESS.  The
distortion caused by the watermark can be restored
without any error.

19. 19
Digital watermarking: problems
- Impossible to have an ideal watermarking scheme.
- If the accuracy is not too high, can the results be still used?
- Can some (advanced) attacks be ignored?
- Configuring a watermarking scheme is very complicated.
- How to balance different objectives?
- Require actions from both vendors and users.
- Vendors provide the feature.
- Users learn and use it properly.
- Somebody needs to keep the secret key and disclose it
when needed.
- …

20. Detecting Lost Identities:
From Digital Watermarking to Multimedia Forensics
Passive Solution:
Multimedia Forensics

21. 21
What is multimedia forensics?
- A new research topic developed since late 1990s.
- Multimedia forensics = Forensic analysis of
multimedia data and devices.
- Source identification = What produced this work?
Was this work computer generated or captured by a
device? Who produced this work?
- Forgery detection = Is this work genuine? Which part of
this work is genuine?
- Processing history recovery = What has happened on
this work? What is the parameter of a step of the
processing history?
- …

22. 22
Better than digital watermarking?
- Yes
- No need to design an (ideal) algorithm.
- No need to configure an algorithm.
- No action required for vendors or users.
- No
- Only limited information can be extracted.
- Accuracy of extracted information could be even lower.
- Often require training = No a prior information about
something, nothing can be extracted about it.
- Anti-forensics can defeat forensics!

23. 23
Identifying authors
- Forensic (behavioural) biometrics
- Like handwritten signatures, intrinsic
features in multimedia work may be
linked to its authors’ identities.
- BBC News, New Vincent van
Gogh painting identified, 9
November 2013
- “The museum said the painting was
authenticated by letters, style and
the physical materials used.”
- All could be identified via some
multimedia forensic techniques.

24. 24
Identifying devices
- Source identification
- Identifying the source device producing a digital
audio/image/video file.
- How can this be done without a watermark?
- Different hardware and software components in different
models
- Different intrinsic features of individual devices (noise
patterns, manufacturing deviations, dust spots and dead
points on camera sensor array, …)

25. 25
Linking devices with authors
- When the device of the author can be obtained.
- Sometimes only the model matters.
- When some other pieces of multimedia work
produced by the same device have their author(s)
identified.
- So “Register Your Sample Work” is important?
- When the device’s intrinsic features are registered
at a trusted party.
- So “Register Your Device” is important?

26. Detecting Lost Identities:
From Digital Watermarking to Multimedia Forensics
Expertise of Researchers @
Surrey Computing

27. 27
MSF Group @ Surrey Computing
- MSF = Multimedia, Security and Forensics
- 6 academics
- Prof Anthony TS Ho (Group Head / HoD)
- Prof Jianmin Jiang
- Dr Johann A Briffa (Lecturer)
- Dr Shujun Li (Senior Lecturer)
- Dr Norman Poh (Lecturer)
- Dr Stephan Wesemeyer (Tutor)
- 1 postdoctoral fellow
- 13 PhD students (including 4 jointly with other
research groups)

28. 28
MSF Group @ Surrey Computing
- Multimedia Security
- Digital and Multimedia Forensics
- Cyber Security and Privacy
- Biometrics and Health Informatics
- Multimedia Coding & Visual Quality
Assessment
- Digital Media Content Analysis
- Big Data Analytics

29. Detecting Lost Identities:
From Digital Watermarking to Multimedia Forensics
Thanks for your attention!
Questions + Answers