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。     

一种变容量的自嵌入图像易碎水印算法

为了减小图像自嵌入水印的长度,降低水印对载体图像质量的影响,同时为消除基于分块的图像认证算法中图像块之间的独立性,提出了一种变容量的自嵌入易碎水印算法:首先对图像进行2×2的分块,根据各分块灰度均值生成原始图像的均值图像;根据均值图像各像素之间的相关性进行游程编码;将编码信息作为水印嵌入在图像像素的最低两位中;篡改检测时首先使用字符串匹配的思想进行图像块和水印之间的匹配,对于未匹配成功的块,使用分组的方式进行再次匹配,以完成认证和恢复.该算法进行一次的水印嵌入,同时用于篡改检测与恢复,水印长度依赖于均值图像相邻像素之间的相关性,可有效缩短水印长度,减小对载体图像质量的影响.理论分析和实验仿真表明,算法在不可见性、篡改定位和恢复、抗拼贴攻击、漏检率等方面具有较好的效果.     

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。     

Self-embedding fragile watermarking algorithm with tamper authentication and content recovery separated

为了提高可恢复水印的认证精度和恢复质量,降低虚警率,提出了一种窜改认证与内容恢复分离的自嵌入水印算法.该算法以2×2的图像块为认证单位,将认证水印与恢复水印分别嵌入到自身图像块和偏移图像块中,使认证虚警率降为0;同时提出一种基于线性函数和混沌映射的偏移值选取方案,使图像的恢复质量得到提高.理论分析和实验结果表明,该算法能在抵抗拼贴和量化攻击的同时,准确定位图像窜改并以较高的质量进行恢复.     

一种改进的基于循环块相关的脆弱水印认证算法

针对一种基于循环块相关的脆弱水印认证算法不能有效抵抗伪认证攻击的安全缺陷,分析并提出了相应的改进算法。首先利用Logestic混沌映射生成基于图像块特征的水印信息;然后采用改进的基于循环块相关的嵌入策略,将图像块水印信息分为两部分并分别嵌入块自身和相关块的最低有效位平面（LSB）;最后对各图像块的LSB进行混沌置乱。实验结果表明,该算法不仅能很好地抵抗伪认证攻击,且具有块独立算法的篡改定位精度,能很好地实现图像认证功能。     

基于Krawtchouk不变矩和小波域的双重数字水印

文章提出一种双重数字水印算法,其利用Krawtchouk不变矩的不变性来对抗几何攻击。该算法首先根据水印比特的长度自适应地小波分解载体图像,嵌入水印通过修改最后一级低频逼近子图系数。其次用含水印图像的Krawtchouk不变矩构造另一重虚拟水印,并在两重水印间建立特定的映射关系,使得在水印受攻击时能得到有效恢复,达到保护版权的目的。实验结果表明,该算法在抵抗几何攻击和联合图像专家组（Joint Photographic Experts Group,JPEG）压缩、裁剪、噪声等常规攻击以及有很好的效果。     

自嵌入全盲鲁棒水印量化算法

为了提高图像水印的实用性,提出了一种自嵌入全盲鲁棒水印算法。首先,对原始图像进行DWT,将小波低频子带分成互不重叠的子块,对每个子块进行DCT,通过比较各个子块的直流系数与所有子块直流系数的均值之间的大小关系来产生特征水印序列,利用分段Logistic混沌序列对特征水印进行加密;然后,将加密后的特征水印序列通过奇偶量化规则自嵌入到原始图像小波低频子带每个子块的DCT低频系数中;最后,进行IDCT合成和IDWT产生含水印图像。该算法通过结合自嵌入加密的特征水印序列和盲提取认证水印序列达到全盲检测。实验结果表明,该算法对抵抗添加噪声、JPEG压缩及高斯低通滤波等常见的图像处理攻击均具有很强的鲁棒性。     

窜改认证与内容恢复分离的自嵌入脆弱水印算法

为了提高可恢复水印的认证精度和恢复质量,降低虚警率,提出了一种窜改认证与内容恢复分离的自嵌入水印算法。该算法以2×2的图像块为认证单位,将认证水印与恢复水印分别嵌入到自身图像块和偏移图像块中,使认证虚警率降为0;同时提出一种基于线性函数和混沌映射的偏移值选取方案,使图像的恢复质量得到提高。理论分析和实验结果表明,该算法能在抵抗拼贴和量化攻击的同时,准确定位图像窜改并以较高的质量进行恢复。     

一种感兴趣区域二维水印算法的实现

针对图像中用户选定的感兴趣区域ROI(Regions of interest)的保护,提出形状自适应离散小波变换SA-DWT(Shape Adaptive DWT)是实现感兴趣区域二维水印算法的有效工具.水印图像(一幅灰度图像)经压缩后生成可以嵌入的水印序列,同时SA-DWT变换作用于ROI区域,通过选择变换系数的嵌入位置和嵌入准则实现水印信息的嵌入;最后提取水印信号,通过重构恢复水印图像.攻击实验表明该算法可以抵抗常见的图像攻击手段,ROI区域得到了有效保护.     

Chaos-based self-embedding fragile watermarking with flexible watermark payload

This paper proposes a self-embedding watermarking scheme that reduces the watermark payload significantly while maintaining good recovery quality and security. The embedded watermark contributes to the tamper detection and content recovery and is composed of only the compression codes of the image content. The compression codes with variable length are generated according to the roughness of the image. To improve the security, a chaos-based pseudorandom sequence generator is adopted to generate block-mapping sequence and encrypt compression codes. The proposed method takes into account the invisibility, recovery quality, and security using the flexible watermark payload, which preserves sufficient information of the image block with as few bits as possible. Experimental results demonstrate that the proposed scheme not only outperforms conventional self-embedding fragile watermarking algorithms in tamper detection and recovery, but also improve the security against the various counterfeiting attacks.     

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)     

Secure variable-capacity self-recovery watermarking scheme

Since existing watermarking schemes usually cannot recover the tampered position, a secure variable-capacity self-recovery watermarking scheme is proposed. Both watermark embedding capacity and security are taken into account. The original image is divided into texture blocks and smooth blocks, and the texture blocks not only save traditional information, and save the “details” information. The so-called “details” information refers to the texture information, which not only can effectively resist mean attack, but also help to improve the quality of the recovered image to meet the needs of practical work. And then according to the characteristics of different blocks, the different length compound watermarks are produced. The so-called “compound watermarks” include the authentication watermarks and information watermarks. Authentication watermarks are used to detect the tampered region, and the information watermarks which include basic watermark and additional watermark are used to recover image. Then the compound watermarks are inserted into the other blocks based on the new proposed scheme called three level secret-key embedding scheme (TLSES). And then detect the tamper blocks and recover them by the three level tamper detection scheme (TLTDS). The experimental results show that the paper can not only accurately detect the tamper region and recover image, but also can effectively resist mean attack and collage attack.

     

基于人工神经网络的半脆弱零水印技术

提出了基于人工神经网络的半脆弱零水印技术。首先在宿主图像中随机选择像素点,然后利用神经网络构建所选择像素点与其3×3邻域像素之间的关系,并与二值水印图像进行异或运算得到水印检测密钥,作为所构造的零水印。由于仅从宿主图像中抽取特征构造水印,而没有向图像中嵌入信息,避免了嵌入水印所导致的图像变形。该技术可以用于图像真实性、完整性认证,并可定位篡改发生的位置,且对于JPEG图像压缩具有一定的稳健性。实验结果证明了算法的有效性。     

A self recoverable dual watermarking scheme for copyright protection and integrity verification

Dual watermarking implies embedding of robust as well as fragile watermarks into the same cover image. It facilitates integration of copyright protection and integrity verification into the same scheme. However, most of such existing state of art approaches either lacked the feature of tamper detection and original content recovery or provided an approximation using coarser block level approach. The proposed self recoverable dual watermarking scheme integrates all the aforementioned functionalities of copyright protection, tamper detection and recovery into one scheme. The scheme is independent of the order of embedding of robust and fragile watermarks as these are embedded in different regions of the cover image. It performs tamper detection and recovery, both at the pixel level. The scheme obtains recovery information for each 2×2 image block in just eight bits which are further encoded to only four bits via mapping table. This reduction in recovery bits allows efficient embedding of copyright information which is tested against comprehensive set of attacks. The scheme is found to be robust against noises, filtering, histogram equalization, rotation, jpeg compression, motion blur etc. Besides the normalized cross correlation value, the evaluation of the extracted copyright information is also being done using various objective error metrics based on mutual relation between pixels, their values and locations respectively. The imperceptibility and visual quality of the watermarked as well as recovered image is found to be satisfactorily high. Three major categories of images: natural, texture as well as satellite have been tested in the proposed scheme. Even minute alterations can be chalked out as the detection accuracy rate has been enumerated on pixel basis. The scheme can tolerate tampering ratios upto 50 percent though the visual quality of the recovered image deteriorates with increasing tampering ratio. Comparative results based on normalized cross correlation, probability of false acceptance, probability of false rejection and peak signal to noise ratio metrics validate the efficacy of the proposed scheme over other existing state of art approaches.     

Block Truncation Coding based effective watermarking scheme for image authentication with recovery capability

Due to the advancement of photo-editing software, powerful computers and high resolution capturing devices, it has become tough to prevent the digital image from tampering. So, in these days just by looking a digital image we cannot say whether it is a genuine or not. This is why digital image authentication, as well as restoration, has become the essential issues, especially when it is utilized in medical science, evidence of court, and forensic science. This paper proposes an effective self-embedding fragile watermarking technique for the digital image authentication as well as recovery. The watermark is generated by quantization, and block truncation coding (BTC) of each 2 × 2 non-overlapping block and embedded in three least significant bits (LSBs) of the corresponding mapped block. The recovery bits are derived from most significant bits (MSBs) of the host image, and the authentication bits are derived from recovery bits, the spatial location of pixels and watermark keys. Even if tempering rate is 50%, the reconstruction of tampered image is achieved with high peak signal-to-noise ratio (PSNR) and normalized correlation coefficient (NCC). The experimental results demonstrate that the proposed scheme not only outperforms high-quality recovery fidelity but also negotiate the blocking artifacts additionally it improves the accuracy of tamper localization due to the use of very small size blocks.

     

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.

     

An efficient fragile watermarking scheme with multilevel tamper detection and recovery based on dynamic domain selection

Self-recoverable fragile watermarking is meant for accurate tamper localization as well as image recovery with superior visual quality. However, most of the existing state of art approaches perform authentication and recovery on block basis owing to which the entire block is categorized as tampered in case of alteration of one or more pixels of it. This, results in staircase formation of tamper detected regions, hence lacking in accuracy. Furthermore, the visual quality of the recovered image also deteriorates as an approximate value is assigned to all the block pixels corresponding to the altered region. The proposed watermarking scheme performs both authentication and recovery pixelwise. The authentication of each pixel is done via multi level tamper detection(MLTD) through three authentication bits based on value, location and neighbourhood information. The domain for image recovery is chosen dynamically based on the content of the block, may it be in spatial domain for smooth blocks or frequency domain for the rough ones. This provides high accuracy in recovery. As the embedding of recovery information is done in the frequency domain, the imperceptibility of the watermarked image scheme remains high. Also, embedding of authentication information in the spatial domain maintains its fragile nature. Even for higher tampering ratios, the lost content is rebuilt with high peak signal to noise ratio(PSNR) of the recovered image. The probabilities of false rejection and false acceptance head towards the ideal value for most of the empirical analysis. Comparative study via metric evaluation of probability of false rejection (PFR), probability of false acceptance (PFA) and PSNR of recovered image for different standard test cover images demonstrate the efficacy of the proposed scheme over other existing state of art approaches. Further, the security of the proposed scheme remains high due to usage of multi-layered secret keys and chaos based random mapping handling worst tamper scenarios.     

精确的图像篡改定位与恢复的三水印算法

针对目前图像篡改定位与恢复的水印算法在篡改定位精度和篡改恢复性能方面存在的不足,提出一种精确的图像篡改定位与恢复的三水印算法。该算法在最低有效位(LSB)方法的基础上,采用二进制编码的方式生成检测水印、定位水印和恢复水印等三种水印,并嵌入到图像的低位。篡改检测和篡改恢复采用基于分块的检测水印和恢复水印,篡改精确定位采用基于单像素的定位水印。仿真实验表明,该算法对任意大小的亮度图像、RGB图像具有高精度的篡改定位能力,并且具有很好的篡改恢复性能。     

抗拼贴攻击的二值图像认证算法

为提高算法抵抗拼贴攻击的能力,本文结合块相关思想提出一种二值图像认证算法.该算法首先将每个图像块中的像素点分为“可翻转”和“不可翻转”两类,将“不可翻转”像素点 Hash 生成水印信息,用其替代相应映射块的“可翻转”像素点实现水印嵌入.通过比较图像块重构水印及提取水印的一致性判断该图像块的真实性,并结合各图像块邻域篡改特征进一步提高篡改检测性能.实验结果表明,该算法不仅提高了在替换、添加、删除攻击下的篡改检测性能,而且能够有效抵抗拼贴攻击.