用于图像认证的变容量恢复水印算法

兼顾水印嵌入容量和安全性,提出一种水印容量可变的数字图像可恢复水印算法.该算法提取2×2图像块特征生成变容量恢复水印——平滑块6比特,纹理块12比特.图像块的恢复水印基于密钥随机嵌入在其它图像块的低有效位,通过比较图像块特征与相应恢复水印重构的块特征并结合邻域特征判定图像块的真实性,变容量恢复水印用尽可能少的比特数保存足够的图像块信息,仅被嵌入一次且同时用于篡改检测与恢复,不仅有效降低了水印嵌入容量,而且提高了算法抵抗恒均值攻击的能力.实验仿真结果表明,该算法得到的含水印图像和恢复图像的质量好,且能有效抵抗拼贴攻击、恒均值攻击等已知伪造攻击.     

应用整数提升小波的图像变容量恢复水印方案

传统的可恢复水印算法往往是通过增加嵌入水印容量来提高篡改图像恢复质量,这将导致嵌入水印后图像质量的下降。针对这一问题,提出使用整数提升小波构建变容量恢复水印算法。该算法根据2×2图像块的纹理特征,使用小波系数生成长度可变的恢复水印,加密后嵌入其他映射图像块低位。使用恢复水印,结合相邻块特征进行篡改图像的检测与恢复。实验结果表明新算法能很好地满足水印不可见性要求,能有效抵抗剪切、拼贴及涂鸦等攻击,能更好地实现篡改图像的恢复。     

安全的变容量恢复水印方案

针对现有水印算法大多无法准确定位并恢复被篡改区域的问题,兼顾水印嵌入容量和安全性,提出了一种安全的变容量恢复水印算法.该算法首先将原始图像分成纹理块和平滑块,纹理块除了保存常规信息外,还保存了"细节"信息,不同块将根据自身特点产生不同长度的"复合水印".所谓"复合水印"是指水印由认证水印和信息水印构成,其中认证水印用于检测篡改区域,信息水印用于恢复图像.然后采用新提出的"3级秘钥嵌入方案"(three level secret-key embedding scheme,TLSES)将图像块的"复合水印"随机嵌入在其他图像块中,再利用"3级篡改检测方案"(three level tamper detection scheme,TLTDS)定位被篡改图像块并进行恢复.实验结果表明,所提出的水印算法不仅能够准确检测篡改区域并恢复图像,而且能够有效地抵抗均值攻击和拼贴攻击.     

基于混沌的图像自恢复安全双水印算法

为提高图像自恢复双水印算法的安全性,提出一种基于混沌的安全双水印算法。该算法首先利用混沌映射将双水印信息加密后再嵌入其他图像块的低位,然后结合图像块内容和嵌入在图像块低位的恢复水印信息,利用混沌映射随机生成用于检测图像块真实性的认证数据。理论分析和实验结果表明该算法在保持篡改恢复质量和不可见性的基础上,有效提高了自恢复双水印算法抵抗内容篡改攻击和字典搜索攻击的能力。     

基于邻域比较的JPEG 脆弱水印算法及性能分析

为提高篡改检测性能和协调安全性与不可见性之间的矛盾,提出一种利用邻域比较判定图像块真实性的JPEG脆弱水印算法.该算法将原始图像分成8×8的图像块,基于图像块保护DCT系数生成的4比特水印基于密钥随机嵌入到其他4个图像块量化步长较小的DCT系数最低位.通过比较该图像块与相应4个水印嵌入块8邻域中不一致图像块个数来判定该图像块的真实性,推导给出一般篡改和拼贴攻击下算法的虚/漏警率,并利用统计实验对理论分析结果进行验证.理论分析和实验统计结果表明,通过比较图像块与其相应水印嵌入块8邻域中不一致图像块个数能够提高篡改检测性能,在量化步长较小DCT系数的最低位嵌入水印,解决了保护DCT系数个数与不可见性之间的矛盾.     

基于等级结构的二值文本图像认证水印算法

针对二值文本图像的结构特点, 定义了度量图像中像素点``可翻转性'的像素扩展差, 在此基础上, 提出了一种基于等级结构的用于图像完整性和所有者认证的脆弱水印算法. 根据等级结构, 将原始图像划分为多等级子块, 然后对各等级子块进行独立的水印生成和嵌入. 根据像素扩展差的大小, 将图像块内的像素点划分为``可翻转'和``不可翻转'像素点. 将混沌调制后的``不可翻转'像素点的值映射为混沌系统的初值, 经过混沌迭代生成水印信号, 然后将水印信号替代``可翻转'的像素点, 完成水印的嵌入. 另外, 在图像的最高级子块中嵌入所有者信息, 实现对所有者的认证. 实验结果表明, 该算法具有良好的视觉透明性, 可对二值图像的均匀区域进行有效保护, 并对图像的内容篡改进行多级检测与定位.     

用于内容认证的半脆弱音频零水印算法

提出了一种可用于版权和内容认证的半脆弱音频零水印算法,该算法提取载体音频的中低频分量构造零水印,确保了水印算法的不可感知性,并可实现盲检测。采用自适应的音频分帧方法,合理地分配了水印图像的像素点,从而提高了算法的篡改定位能力和对于常规攻击的鲁棒性。同时利用多级置乱技术消除水印图像的相关性,提高了算法的安全性以及对于常规攻击的鲁棒性。算法不但可进行完整性认证,还可以通过篡改评估准确定位篡改区域。实验结果表明,该算法对于常规攻击具有较好的鲁棒性,对恶意攻击还体现了很强的篡改定位能力。     

基于均值运算和系数分类的半脆弱水印算法

提出一种基于均值运算和系数分类的半脆弱水印算法。在空域对原始图像进行分块,根据每个子块均值运算所得矩阵系数小数部分的规律性将系数分为2类。将图像各像素的高4 bit向右移位,通过每一子块2类系数的个数比较产生零水印。利用篡改前后每类系数个数的不一致性检测算法的篡改定位能力。实验结果表明,该算法的不可见性和鲁棒性较好,能抵抗常规图像处理操作,且具有定位篡改的能力,漏警概率低,能抗拼贴攻击。     

一种安全的基于层次结构的图像认证算法

很多图像认证算法或者篡改定位精度较高,但容易受到攻击,或者牺牲定位精度来提高安全性.该算法利用自定义的层次结构,不但可以抵抗矢量量化(VQ)、黑盒(ORACLE)等各种攻击,满足安全性要求,而且具有很高篡改定位精度.如果一个被篡改的像素在第四层没有被检测出来,也会以将近100%的概率在第三、第二和第一层检测出来.理论分析表明该算法对单像素、2×2像素块篡改的漏报率分别低于0.78%、0.19%,对大于等于4×4像素块篡改的漏报率约等于0.实验结果表明,该算法对图像篡改具有高度的敏感性,而且嵌入的水印具有很好的不可感知性.     

一种篡改检测与篡改定位分离的图像认证方案

针对脆弱水印认证算法的篡改定位精度及安全性问题,提出了一种将篡改检测和定位分离的图像认证方案:对图像进行单像素置乱并将其低两位置零,采用像素关联技术生成各个像素的篡改定位水印,并将其嵌入到自身的次低位;将图像逆置乱后并进行分块,生成各个分块的篡改检测水印,将篡改检测水印嵌入到各像素的最低位,进而生成含水印图像.理论分析和实验结果表明:该方案可以抵抗目前针对单像素认证算法的Oracle攻击及针对分块算法的量化攻击,在保证系统安全性的同时可将篡改定位到单个像素.     

A semi-fragile image watermarking algorithm with two-stage detection

The ability against the collage attack of semi-fragile watermarking is improved by embedding the watermark of a block in other blocks, but the tamper detection performance is impaired under general tampering. A two-stage detection method is proposed to improve the tamper detection performance of semi-fragile watermarking. For each 8 × 8 block, six-bit watermark data generated by the significant DCT (Discrete Cosine Transformation) coefficients are divided into two parts with the same length: general tampering watermark (GTW) and collage attack watermark (CAW). The GTW and CAW data of a block are embedded in the quantized DCT coefficients of itself and other blocks, respectively. In the first-stage detection, the general tampered regions are localized by the GTW data. To identify whether the collage attack exists in the received image, the identification parameter is defined by both GTW and CAW data. The selection of the predefined threshold of the identification parameter is derived and verified by the statistical experiments. If the identification parameter is larger than the given threshold, the second stage detection is performed to detect the collaged regions. Experimental results demonstrate that the proposed two-stage detection method is able to identify tampering with high probability under general tampering, collage attack and hybrid attack.     

A digital authentication watermarking scheme for JPEG images with superior localization and security

The drawbacks of the current authentication watermarking schemes for JPEG images, which are inferior localization and the security flaws, are firstly analyzed in this paper. Then, two counterferiting attacks are conducted on them. To overcome these drawbacks, a new digital authentication watermarking scheme for JPEG images with superior localization and security is proposed. Moreover, the probabilities of tamper detection and false detection are deduced under region tampering and collage attack separately. For each image block, the proposed scheme keeps four middle frequency points fixed to embed the watermark, and utilizes the rest of the DCT coefficients to generate 4 bits of watermark information. During the embedding process, each watermark bit is embedded in another image block that is selected by its corresponding secret key. Since four blocks are randomly selected for the watermark embedding of each block, the non-deterministic dependence among the image blocks is established so as to resist collage attack completely. At the receiver, according to judging of the extracted 4 bits of watermark information and the corresponding 9-neighbourhood system, the proposed scheme could discriminate whether the image block is tampered or not. Owing to the diminishing of false detection and the holding of tamper detection, we improve the accuracy of localization in the authentication process. Theoretic analysis and simulation results have proved that the proposed algorithm not only has superior localization, but also enhances the systematic security obviously. Supported by the National Natural Science Foundation of China (Grant No. 60572027), the Program for New Century Excellent Talents in University of China (Grant No. NCET-05-0794), the Sichuan Youth Science & Technology Foundation (Grant No. 03ZQ026-033), the National Defense Pre-research Foundation of China (Grant No. 51430804QT2201) and the Application Basic Foundation of Sichuan Province, China (Grant No. 2006 J13-10)     

一种分块压缩感知观测值的图像篡改认证算法

文章针对压缩感知理论特点,提出一种新的算法。分块认证可将篡改定位到分块级别,具有较高的篡改定位准确度。算法首先将图像分成若干块,分块大小可以由篡改定位调整,然后对各个分块进行观测得到压缩的观测值。在观测域中将得到的观测值进行LDPC编码生成水印,并将水印嵌入到分块图像中。水印提取时同样对篡改后的图像进行随机投影,对提取的水印进行解码和比较,实现了图像的篡改检测与图像认证。根据实验研究证实,该算法对局部篡改的检测功能较强,算法实现简单且提取过程更加安全。     

一种改进的DWT域图像篡改检测算法

改进一种DWT域图像篡改检测算法。该算法将置乱的有意义的二值水印图像利用量化的方法隐藏在载体图像Haar小波变换系数中。图像认证时,对提取的水印和原水印图像的差值图像进行反混沌置乱,再进行形态学处理,从中可以看出认证图像的篡改区域。此算法与Kunder等人提出的基于Haar小波的半易损水印算法相比,能够有效地区分JPEG压缩和恶意篡改,不需要设置阈值来区分JPEG压缩和恶意篡改,可以从水印差值图像直接看出恶意篡改的区域。     

Stereo image watermarking scheme for authentication with self-recovery capability using inter-view reference sharing

Advances in three dimensional video is a strong stimulus for research in authentication of stereo image to avoid illegal modification. In this paper, a stereo image watermarking scheme is proposed for authentication with self-recovery capability using inter-view reference sharing. A mechanism of inter-view reference sharing in stereo image pairs is designed to reduce bits for recovery reference generation compared with independent references. Discrete wavelet transform coefficients are employed to generate the references, and two reference copies of each block embedded in two different mapping blocks are prepared for recover tamper. Moreover, detail information from high frequency coefficients is also embedded so as to improve the quality of tamper recovery. For the purpose of resisting collage attack and increasing the probability of tamper detection, disparities between pairs of matched blocks are checked to conduct tamper detection. Experimental results show that the proposed scheme can detect tampered blocks with the probabilities of more than 99 % after collage attack. When stereo images are cropped from 10 to 70 % with randomly tampering, they are recovered without losing main visual information and qualities of recovery are better than those of existing monocular image watermarking schemes extended to stereo images.     

低频快速切比雪夫矩的篡改图像检测算法

针对图像复制粘贴篡改的检测及篡改区域定位的研究,提出了一种低频快速切比雪夫矩的篡改图像检测算法.首先用非抽样小波变换对图像分解,选取图像的低频部分进行重叠分块,提取改进的低频快速切比雪夫矩做为特征向量,然后采用PatchMatch算法对提取的块特征匹配,最后用稠密线性拟合算法去除误匹配并且用形态学操作完成最后的篡改区域定位.与现有的篡改图像检测算法相比,所提出的算法对于单区域篡改、单区域多次篡改以及多区域篡改均具有较好的定位效果,并且减少了算法的运行时间,提高了实时性.     

A novel hash function based fragile watermarking method for image integrity

In recent years, tampering and altering of digital images have become easier with the rapid development of computer technologies such as digital image editing tools. Therefore, verification of image integrity and tamper detection of digital images have become a great challenge. Fragile watermarking is the most widely used method for protecting the integrity and content authenticity of the image. In this paper, by using SHA-256 hash function, a novel block based fragile watermark embedding and tamper detection method is proposed. In watermark embedding phase, host image is divided into 32?×?32 non-overlapped blocks. Each 32?×?32 block is then divided into four 16?×?16 nonoverlapped sub-blocks. The entire hash value of the first three sub-blocks is generated as a watermark using SHA-256 hash function. The generated 256-bit binary watermark is embedded into the least significant bits (LSBs) of the fourth sub-block and watermarked image is obtained. In tamper detection phase, the detection of tampered block has been performed by comparing the hash value obtained from the three sub-blocks with the extracted watermark from the fourth sub-block of the watermarked image. The performance of the proposed method has been evaluated by applying linear and nonlinear attacks to the different regions of the watermarked images. Experimental results show that the proposed method detects all the tampered regions of the attacked images and high visual quality of watermarked images has been obtained.