CAC ANNUAL MEETING DATA HIDING IN COMPRESSED MULTIMEDIA SIGNALS Bijan Mobasseri, PI S. R. Nelatury...

CAC ANNUAL MEETING

DATA HIDING IN COMPRESSED MULTIMEDIA SIGNALS

Bijan Mobasseri, PIS. R. NelaturyDom CinalliDan CrossAaron EvansColin O’Connor Sathya Akunuru

ECE DepartmentVillanova UniversityVillanova, PA 19085

October 30, 2002

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Background info

• Funding agency: The US Air Force Office of Scientific Research(AFOSR)

• Monitor: AFRL/IFEC, Information Directorate, Rome, NY

• Project: Smart Digital Video• PI: Bijan Mobasseri

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Outline

• Data hiding/watermarking requirements• Established watermarking approaches• Project summaries:

– Compressed media watermarking– Video authentication through self-watermarking– Lossless watermarking using error-resilient coding– Time-frequency watermarking– Metadata embedding

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Data hiding/watermarking requirements

• Data hiding must at least meet the following three conditions:– Transparency; no visible impact on cover signal– Robustness; filtering, compression, cropping– Security; must assume the algorithm is known

• Places to hide data are:– Spatial- pixel amplitudes, LSB, QIM– Transform domain- spread spectrum, Fourier/wavelet, LPM– Joint- time/frequency distribution

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Applications of watermarking

• Here are few, and growing list– Copyright protection- prevent unauthorized duplication– Fingerprinting-to find out who gave it away– Copy protection- to keep a tab on the number of copies

made– Broadcast monitoring- automatic monitoring of commercials– Authentication- insuring data integrity and tamper

resistance/detection– Indexing- helping multimedia search capability– Metadata hiding- embedding patient’s records in their

medical images– Data hiding- covert communications in plain sight

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Basic idea

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Watermark Embedding and Extraction

• Cover image: f• Watermark: w• Embedding

function:E• Secret key:kStego image=S=E(f,w,k)

• AuthenticationT(S): tampered

signal

ˆ w =g(T (S))

ρ=<w, ˆ w >

ρ>Threshold ⇒

watermark present

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Detector response to forgeries

• Let’s say someone attempts to forge a watermarked document using their own signature

• We then have

• None of the two terms register significant response

Iw =I +kW*

λ =<Iw,W x,y( )>=

< I +kW *( ),W >=

<I,W >+k <W,W * >

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Block Diagram

• Embedding

• Watermark extraction

SOURCEWATER

MARKING

TAMPERINGCORRUPTED WM SOURCE

CORRUPTED WM SOURCE -

SOURCE

DISTORTEDWM X

ORIGINALWM

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Quality of extracted watermark

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Trade-offs

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LSB watermarking

• Probably the earliest attempt at watermarking was to flip the least significant bit of each pixel

• LSB being at noise level, would have no impact on quality. However, the slightest change in pixel intensity would make the watermark unreadable

Pixel 1 Pixel 2

LSB

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BITPLANE WATERMAKRING

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Hiding information in 24 bit images

• A 1024x768 24-bit color image can potentially hide 2,359,296 bits

• How would you hide the letter A? “A” can be hidden in the LSB of 3 pixels such as

• The binary value of A is 10000011. Changed bits are shown

00100111 11101001 1100100000100111 11001000 1110100111001000 00100111 11101001

00100111 11101000 1100100000100111 11001000 1110100111001000 00100111 11101001

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Transform domain watermarking

• Spatial watermarking is fast but brittle.• It is best to do watermarking in

transformed domains DFT– DCT– DWT

• The first successful implementation was done by Cox et al at NEC/Princeton under spread spectrum watermarking

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Basic idea

• Instead of tweaking pixels, alter selected coefficients of image transform

• Then do inverse transform. This way, watermark spreads throughout the image affecting every pixel in some way

• It is not possible to find the watermark in the spatial domain

1 2 3 4 5 6 7 8

1

2

3

4

5

6

7

8

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SPREAD SPECTRUM WATERMARKING(Cox, NEC)

555555 55555555 55555555 55

555555 55

DCT

550 10 -1 0

2 3 2 0

-1 2 0 0

0 0 0 0

16 1 0 0

0 -1 0 0

-1 2 0 0

0 0 0 0

Quan

16 1 -1 0

1 -1 0 0

-1 2 0 0

0 0 0 0

Original frame

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Challenges

• Which DCT coefficients should you choose?

• We have to worry about two competing requirements– Robustness - means low

frequency terms should be modified

– Imperceptibility - means low frequency terms should be avoided

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DFT watermarking

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Watermarking DWT

VIDEO WATERMAKING

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Tampering scenarios: cut and splice of surveillance video

• A block of frames removed and video spliced

• Video must be embedded with proper sequencing codes so as to reveal the breakage

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Cut, insert and splice

• Incriminating/sensitive portion is removed and replaced

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Cut, swap and splice

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Collusion attack

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MPEG bitstream syntax

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Embedding watermark bits in VLCs

• Variable length codes are the lynchpin of MPEG

• There is a subset of MPEG VLC codes that represent identical runs but differ in level by

just one

From: Langelaar et al, IEEE SP Magazine

September 2000

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Data hiding capacities

Total lc-VLCs Total VLCs24008 204493

655548 4321760

61298 461027

3614 61985

345315 3290373

24412 204362

run 0 0 0 0 0 0 0level 5 6 8 9 10 11 12406974ai1.mpeg 3734 2630 1835 1423 1122 827 1036% occurrence 15.6 11.0 7.6 5.9 4.7 3.4 4.3status.mpeg 136422 90706 60594 46844 36066 32513 25822% occurrence 20.8 13.8 9.2 7.1 5.5 5.0 3.9avalon.mpeg 13080 9506 5420 4353 3405 2865 2341% occurrence 21.3 15.5 8.8 7.1 5.6 4.7 3.8gtscrush.mpeg 1056 700 281 246 193 131 143% occurrence 29.2 19.4 7.8 6.8 5.3 3.6 4.0final-days.mpg 78900 54245 30487 24116 18751 15464 12791% occurrence 22.8 15.7 8.8 7.0 5.4 4.5 3.7simp.mpg 5997 4007 2438 1441 1627 1225 807% occurrence 24.6 16.4 10.0 5.9 6.7 5.0 3.3

average % occurrence 22.4 15.3 8.7 6.6 5.5 4.4 3.8

SELF-WATERMARKING*

*D. Cross, B. Mobasseri, “Watermarking for self-authentication of compressed video,” IEEE ICIP2002,

Rochester, NY, September 22-25, 2002,

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Self-watermarking:the concept

• In self-watermarking, the watermark is extracted from the source itself

• Self-watermarking prevents watermark pirating

• Most work on self-watermarking has been done on images.

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Self-watermarking of compressed video

1 0

VLC(0,5)

VLC(0,16)

VLC(1,15)

VLC(0,6)

VLC(1,10)

VLC(1,11)

VLC(0,12)

Lossless Watermarking of Compressed Media*

*B. Mobasseri, D. Cinalli “Watermarking of Compressed Multimedia using Error-Resilient VLCs,” MMSP02, December 9-11, 2002

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The idea:watermark as intentional bit errors

• A close look reveals that watermarking of VLCs is essentially equivalent to channel errors.

• Bit errors and watermark bits have identical impact. They both cause bit errors in affected VLCs.

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The solution:lossless watermarking

• Embed watermark bits in the VLCs as controlled bit errors

• MPEG-2 VLCs, however, have no inherent error protection. Any bit error will cause detection failure up to start code

• Bidirectionally decodable codewords are capable of isolating and reversing channel errors

• This approach leads to lossless watermarking

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Bi-directional VLCs

• Each VLC is represented twice in the new bitstream. It is this property that allows error resiliency

• Burst error shall not be so long to simultaneously affect the same bit of identical VLC

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Watermarking capacity

• If watermarking begins with the first bit of the VLC and L=l, every bit of the VLC may be watermarked, then

C=L bits/packet• We define packet as one

macroblock

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Data

Non- Coded MBsVideo # Coded MBs

Intra & InterInter Skipped

Avg. # ofVLCs / MB

Avg. # ofBits / MB

Avg. % increase insize per MB with

thresholdCapacity

1 902 7,153 45 4.83 25.33 .87% 4,5102 57,326 66,162 40,240 8.02 42.07 13.6% 286,6303 309,740 99,981 42,391 15.38 76.76 18.89% 1,548,700

TIME-FREQUENCY WATERMARKING

B. Mobasseri, “Digital watermarking in joint time-frequency domain,”,IEEE ICIP, Rochester, NY, September, 22-25, 2002

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The Idea

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TF watermarking

0 10 20 30 40 50 60 70 80-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

-3

0

20

40

60

80

100

120

140

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

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x 105

original WVD

€

Wx nT , f( ) = 2T x n + m( )m∑ x* n −m( ) exp(− j4πfmT ), f ≤

1

4T

WD +

€

Y t, f( ) = X t, f( ) + w t, f( ); t , f ∈Ω{ }

D

WD-1

0 10 20 30 40 50 60 70 80-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

-3

WD

0

20

40

60

80

100

120

140

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

-505

x 105

original WVD

WM

JPEG

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Results

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Effect of compression

JPEG:Q=5

Metadata Embedding

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Background

• Video images & metadata recorded and handled as two separate streams

– Storage overhead– Bookkeeping issues– Accuracy and human error– Cumbersome to display

• It would be nice to permanently attach metadata to video and make it available during playback

MetadataVideo

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Sample Metadata and video footage

Surveillance VideoXML Coded Metadata

THE END