5/8/01

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Standards Compliant Watermarking for Access Management

Viresh Ratnakar & Onur G.Gulyeruz

Please view in full screen presentation

mode to see the animations.

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Visible Watermarks for Digital Images: Traditional Schemes—Logos

An identifying logo in a corner

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Visible Watermarks for Digital Images: Traditional Schemes—Blended Marks

Unobtrusive visible watermarks aimed at asserting ownership or authenticity

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Our Goal: Obtrusive visible watermarks that can be removed

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Obtrusive watermarks that can be removed

Similar to scrambling, except that only parts of the image (located on a distinctive pattern) are modified

Example application: user retrieves a watermarked image over the net, pays $$ to print, the printing driver removes the watermark just for printing

Simple for un-lossy-compressed images:Y = X R

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Desired scrambling and descrambling pipeline for compressed images

JPEG Image

Key K

S

Scrambler

EWatermarked JPEG

ImageD

DeScrambler

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Format compliance, compression

The XOR idea does not survive lossy JPEG compression

The watermarked image should be format compliant, i.e., in JPEG format

For such completely removable watermarks on JPEG images, we must work with and modify quantized DCT coefficients, not pixels

The size of the watermarked image, ideally, should be no more than the original

We achieve all these goals with the proposed algorithm, DctDots

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DctDots: Apply corruption to the blocks which lie on the pattern

F0,0 F0,1 F0,4 F0,5

F0,2 F0,3 F0,6 F0,7

F0,40 F0,41 F0,44 F0,45

F0,42 F0,43 F0,46 F0,47

F1,0 F1,1

F1,2 F1,3

F2,0 F2,1

F2,2 F2,3

Y (Luminance)

Cb (Chrominance)

Cr (Chrominance)

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DctDots: Four “tricks” for corrupting blocks

1. AC Masks: XOR the AC coefficient magnitude bits

2. AC Swaps: Swap AC coefficient blocks

3. DC Shuffles: Shuffle DC differentials within

contiguous pattern blocks

4. DC Bit Shuffles: Shuffle DC differentials within

contiguous pattern blocks

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AC coefficients are coded as

Bits in H are the Huffman code for

(run = R, magnitude-category = S),

Bits in V are the S magnitude bits (1’s complement)

We apply XOR (with a keyed PRNG) to just the bits in V, thus maintaining format-compliance and ensuring that the size is not changed

1. AC Masks

H V

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2. AC Swaps

Within a color component, entire blocks of AC coefficients (i.e., the 63 coefficients excluding the DC) can be swapped across blocks lying on the pattern.

The swapping is determined by the PRNG, hence reversible.

Format compliant Size does not increase

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3. DC Shuffles

Quantized DC coefficients are differentially coded, hence tricky

Work with consecutive sequences of blocks to be modified (i.e., on the pattern)

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3. DC Shuffles – Contd.

Shuffle the differntial quantized DC values within such a pink sequence

Size does not increase at all The last block in the sequence undergoes

no change to its DC value (thus, include the first white block after the pink sequence in the shuffling)

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4. DC Bit Shuffles

This step supplements the DC shuffling step—it also works with the differential DC values from the pink blocks

In this step, we go down to the bit planes of the differential DC term

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4. DC Bit Shuffles – Contd.

X 1 0 0 1 1 0 1

X X X X 0 0 1 1

X X X X X 0 0 0

X 1 0 1

X X X 0 1 0 0 0

X X 0 0 1 0 0 0

X X X X X X X X

X 0 1 1 1 1 0 1

X X 1 1 0 0 1 0

X X X X

Blocks

Bit Plane

0

1

0

1

0

1

X

0

0

0

1

1

0

0

1

X

0

0

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DctDots: Example Result

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Conclusion

Different goals compared to traditional visible watermarking

DctDots: Format compliant watermarking technique for obtrusive, visible, removable watermarks on JPEG images

Compressed size is exactly the same Extension to video—only in restricted cases.