protect the rights of their owners

Copyright identification
User identification or fingerprinting
Authenticity determination
Automated monitoring
Copy protection

조건

추가된 워터마크는 눈에 보이지 않아야 함
어 떤 경우에서던지 제거할수 없이 강력하여야 함
저작자의 정보를 내장
내장된 디지털워터마크는 복잡해야 한다.

visible watermark

Invisible Watermark

깨지기 쉬운 워터마크

강력한 워터 마크

compression, filtering cropping, rotation, resampling, additional watermark or noise
A typical image watermarking system

DCT-based watermarking

Mark insertion

Setp1 : 2-D DCT of the image

Setp2 : Locate its K largest coefficients,, by magnitude

Setp3 : Create a watermark by generating a K-element pseudo-random sequence of numbers,, taken from a Gaussian distribution.

Setp4

:

Setp5 : Inverse DCT of the result from step 4

Mark extraction

Setp1 : 2-D DCT of the image

Setp2 : Extract the K DCT coefficients

otherwise : unmarked or different watermark

Setp3 :

Setp4

: Measure the similarity

Setp5