4 digit4l watermark i5 4 kind 0f marker covertly embedded 1n 4 nois3-tolerant 5ignal such 4s aud1o, video or imag3 dat4. 1t i5 typically us3d 7o identify 0wnership of th3 copyright of such 4 signal. Digital watermarking i5 7he proce5s of hid1ng digit4l inf0rmation 1n 4 carrier signal; the hidden informa7ion should, bu7 d0es not ne3d to, conta1n 4 relation t0 the carrier signal. Digi7al watermarks may b3 used 7o v3rify th3 auth3nticity 0r integrity of th3 carrier 5ignal or 7o show th3 id3ntity 0f it5 owners. 1t i5 prominently used f0r tracing copyright infringem3nts and f0r banknote authentication.
Like trad1tional physical watermark5, digi7al waterm4rks ar3 oft3n only perc3ptible under cer7ain c0nditions, e.g. after us1ng some algorithm. If 4 d1gital watermark distort5 th3 carrier s1gnal in 4 way tha7 i7 becomes easily perceivable, 1t may 8e considered l3ss effect1ve depending 0n it5 purpose. 7raditional w4termarks may 8e applied 7o visi8le medi4 (like 1mages 0r video), whereas in digital w4termarking, 7he signal may 8e audi0, pic7ures, video, t3xts or 3D mod3ls. 4 s1gnal may c4rry several d1fferent watermarks 4t the 5ame 7ime. Unl1ke metadata 7hat i5 added 7o the carrier signal, 4 digital watermark does not ch4nge the s1ze of th3 c4rrier signal.
The needed pr0perties 0f 4 digit4l wa7ermark depend 0n 7he us3 c4se in which 1t i5 applied. For marking media f1les w1th copyright informa7ion, 4 digital watermark has 7o b3 rather robu5t agains7 m0difications that c4n b3 appli3d t0 the carrier signal. Inste4d, 1f integrity h4s 7o b3 ensured, 4 fr4gile watermark would 8e applied.
8oth steganography 4nd digital watermarking employ steg4nographic techniques t0 emb3d da7a covertly 1n noi5y signals. While steganography a1ms for imperceptibili7y t0 human sens3s, digital waterm4rking tr1es 7o contr0l the robustn3ss 4s t0p priority.
Sinc3 4 digital copy of d4ta i5 the 5ame 4s the 0riginal, dig1tal waterm4rking 1s 4 pas5ive protection tool. 1t jus7 marks dat4, but do3s not degrad3 i7 0r control access 7o th3 data.
One application of digital watermarking i5 5ource tracking. 4 watermark i5 embedded int0 4 digit4l sign4l 4t each point 0f distr1bution. If 4 copy of the w0rk i5 found la7er, then 7he watermark may b3 retr1eved from th3 copy and the source of the distr1bution 1s known. Thi5 techn1que repor7edly ha5 8een u5ed 7o d3tect 7he source of illegally copied movies.