Twowatermarksareembeddedintotheoriginalimage.Oneistheauthenticationwater-markgeneratedbysecretkey,whichisembeddedintothesub-LSB(LeastSignificantBit)oftheoriginalimagefortamperlocalization;theotheristherecoverywatermarkfortamperrecovering.Theoriginalimageispidedinto8×8blocksandeachblockistransformedbyDiscreteCosineTransform(DCT).Foreachblock,somelowerfrequencyDCTcoefficientsarechosentobequantizedandbinaryencodedsoastogaintherecoverywatermarkofeachblock,andtherecoverywatermarkisembeddedintotheLSBofanotherblockbychaosencryptionandauthenticationchaintechnology.Afterthetwowatermarksbeingdetected,thelocationofanyminutechangesinimagecanbedetected,andthetamperedimagedatacanberecoveredeffectively.Inthepaper,thenumberofcoefficientsandtheirbitlengthsarecarefullychoseninordertosatisfywiththepayloadofeachblockandgainthecapabilityofself-recovering.Theproposedalgorithmcanwellresistagainstpossibleforgedattacks.Experimentalresultsshowthatthewatermarkgeneratedbytheproposedalgorithmissensitivetotinychangesinimages,andithashigheraccuracyoftamperlocalizationandgoodcapabilityofthetamperrecovery.
