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.

     

一种基于Hash函数的脆弱水印算法

当前空域脆弱水印算法存在安全性不高及不能有效抵抗矢量量化攻击的缺陷。针对该缺陷,提出一种用于数字图像完整性认证及内容篡改证明的脆弱水印算法。算法首先对图像进行8×8分块,利用Logistic混沌映射对图像分块进行置乱编号;再采用Hash函数生成基于图像分块内容和位置信息的水印信号;最后将水印信号嵌入到图像分块像素值的低两位平面。实验结果及理论分析表明,提出的脆弱水印算法在保证安全性的同时,有效地抵抗了矢量量化攻击。     

一种基于混沌Hash函数的脆弱水印算法

针对现有分块脆弱水印的缺陷,提出了一种基于混沌Hash函数的脆弱水印算法。该方案通过将原始图像分块后做混沌Hash,生成原始图像的摘要,与由混沌映射生成的混沌二值图像异或后生成二值脆弱水印,置乱加密后嵌入原始图像的LSB平面;认证时通过差值图像定位篡改的区域。理论分析和实验仿真表明提出的水印算法不可见性好,能够有效抵抗VQ攻击,并能够区分篡改的类型,安全性高。     

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.     

基于DCT的半脆弱水印算法

数字水印技术成为多媒体信息安全研究领域的一个热点问题.对变换域DCT(discrete cosine transform)域的半脆弱性的数字水印算法进行了研究.该算法首先生成数字水印:水印图像是灰度图,根据特定的分组表及公式将所有系数进行分组,进而生成二进制水印信息;然后将宿主图像进行基于分块DCT变换,最后将水印信息嵌入到各分块DCT域的中低频系数中.该算法对一些常见的图像处理具有一定的鲁棒性,同时具有一定的检测篡改的能力,可以定位到空间域的8*8块.试验结果验证了该方法的有效性.     

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.     

一种小波域内的鲁棒脆弱图像水印技术

目前的水印算法有鲁棒水印和脆弱水印两类,分别可以用于图像的版权保护和篡改检测,但很少有算法能够结合两者,同时实现这两种功能。为了解决这一问题,该文提出一种鲁棒-脆弱水印算法：首先在小波变换图像的逼近子带中,利用系数间的关系构造特征水印;然后根据小波零树思想,结合主分量分析,采用抖动调制方法嵌人到重要小波树的第一主分量中;水印检测时,将提取的特征水印与嵌入水印进行比较,不仅可以确定图像的版权,还可以证明内容的完整性。实验结果表明,此算法能够抵抗滤波、压缩、叠加噪声等处理,同时还可以很好的定位图像的篡改,是一种很有效的水印算法。     

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.     

自嵌入空域易损水印技术

提出了一种新颖的自嵌入易损水印技术用于图像的完整性认证．提出引入基于图像的不确定性来克服其他算法中存在的安全缺陷．通过结合图像特征及相机密钥来产生基于图像的密钥来实现这一目的．相机密钥的惟一性解决了密钥的管理问题．算法把图像本身的信息作为水印嵌入，认证时可直接进行而不需要其他的水印参照信息．给出了性能分析，表明当嵌入的信息量较大时可以得到较高的篡改检测概率．分析了可能的攻击方式并给出了相应的攻击概率和检测概率．实验结果表明该算法是有效的．     

A self-recovery fragile watermarking scheme for image authentication with superior localization

To address the problems of the inferior localization and high probability of false rejection in existing self-recovery fragile watermarking algorithms, this paper proposes a new self-recovery fragile watermarking scheme with superior localization, and further discusses the probability of false rejection （PFR） and the probability of false acceptance （PFA） of the proposed scheme. Moreover, four measurements are defined to evaluate the quality of a recovered image. In the proposed algorithm, the original image is divided into 2×2 blocks to improve localization precision and decrease PFR under occurrence of random tampering. The PFR under occurrence of region tampering can be effectively decreased by randomly embedding the watermark of each block in conjunction with a novel method of tamper detection. Compared with the current self-recovery fragile watermarking algorithms, the proposed scheme not only resolves the tamper detection problem of self-embedding watermarking, but also improves the robustness against the random tampering of self-embedding watermarking. In addition, the subjective measurements are provided to evaluate the performance of the self-recovery watermarking schemes for image authentication.     

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.     

An improved method for digital image fragile watermarking based on chaotic maps

In this paper, the digital image fragile watermarking method based on chaotic maps is proposed. Our method has some significant advantageous in comparison with other available methods. Firstly, we reduce watermark payloads, while they have high quality of recovery and security. In watermark embedding phase, we process the image in order to produce the information array for each block, which finally embedded in the host image to build watermarked image. The information array for each block has different length, which is defined based on block characteristic that could be smooth or rough. The second superiority of the proposed method is proposing a new metric for calculating roughness of image block, which leads to less consume of bandwidth in comparison with other available methods. Finally, we use chaotic map for block-mapping that enhances the security. Our method provides basic requirements of watermarking scheme such as, invisibility, recover quality and security. Experimental Results have proved that our method is powerful in tamper detection, self-recovery and robust against known watermarking attacks.     

A novel self-recovery fragile watermarking scheme based on dual-redundant-ring structure

In this paper, we propose a novel self-recovery watermarking scheme based on dual-redundant-ring structure (DRRS). All blocks of target image form a ring in a manner that the watermark of an image block is hidden in 1-LSB (least significant bit) of its next block N₁, and the copy of this watermark is embedded into 2-LSB of another block whose position is determined by the position of N₁. The validity of test image block is determined by comparing the number of inconsistent blocks in the block-neighborhood with that of its mapping block. Other detection result is generated in the same way comparing test block with copy block of its next block. The fusion of two detection marks improves tamper detection accuracy, while two copies of watermark provide a second chance for tamper recovery. Experimental results demonstrate that the proposed algorithm is superior to the state of the art of tamper detection and tamper recovery and could keep high security strength.     

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.     

基于RS码的二值图像认证及篡改定位算法

用于二值图像内容认证和篡改定位的数字水印技术具有重要的实际价值,但却面临着二值图像像素单一、嵌入容量有限且分布不均匀等问题.根据纠错码--RS码的检错原理,提出一种用于二值图像内容认证和篡改定位的脆弱的数字水印算法.该算法利用二值图像的像素值来构造RS码,通过嵌入其校验码来实现对图像的内容认证和篡改定位,一方面保证了其优越的检错能力;另一方面,具有较低的嵌入负载.经实验证明,该算法能有效地检测出二值图像是否被篡改以及篡改发生的位置.此外,在水印信号的生成和提取过程中使用了密钥,确保了水印的安全.     

基于DCT变换的脆弱水印技术

提出了一种用于图像鉴定的脆弱水印方法。该方法首先对图像进行8×8分块,计算每一块的DCT值,然后选择所要保护的区域,确定完全属于该区域的分块,并提取这些分块的特定位置的低频分量,采用Hash函数加密生成相应的具有固定长度的数字摘要,然后选取该数字摘要的若干位作为脆弱水印,并把其隐藏到该区域其余的DCT分块中去,以实现水印检测时不需要任何额外信息,试验表明这是一种行之有效的图像鉴别方法。     

基于混沌和脆弱水印的图像篡改检测算法

针对现有基于脆弱水印方法的不足,提出了一种新的结合混沌系统和脆弱水印的图像篡改检测算法。算法首先利用Arnold cat映射对原始图像进行k次置乱,然后选取置乱图像的最低有效位(LSB)平面作为水印嵌入位置,实际嵌入的水印由Logistic混沌映射产生的随机二进制序列与原始水印异或得到,通过LSB替换算法嵌入。最后对LSB替换后图像进行T-k次的Arnold cat映射得到水印图像。实验结果表明,混沌系统的引入大大增强了脆弱水印的安全性;另外,针对不同种类的攻击,算法具有良好的篡改检测和定位精确性。     

以图像认证为目的的分形编码数字水印算法

以图像认证为目的,提出一种基于分形编码的脆弱性盲水印算法。该算法将认证水印嵌入分形变换域,又将分形编码参数作为水印嵌入到宿主图像中。算法能有效的检测图像是否被恶意篡改,并能定位篡改区域。通过提取嵌入在图像中的分形编码参数,还可以自动恢复被篡改区域。实验数据表明,算法可行有效,并且具有良好的篡改定位和恢复原图像的能力。     

Hybrid watermarking of medical images for ROI authentication and recovery

Medical image data require strict security, confidentiality and integrity. To achieve these stringent requirements, we propose a hybrid watermarking method which embeds a robust watermark in the region of non-interest (RONI) for achieving security and confidentiality, while integrity control is achieved by inserting a fragile watermark into the region of the interest (ROI). First the information to be modified in ROI is separated and is inserted into RONI, which later is used in recovery of the original ROI. Secondly, to avoid the underflow and overflow, a location map is generated for embedding the watermark block-wise by leaving the suspected blocks. This avoids the preprocessing step of histogram modification. The image visual quality, as well as tamper localization, is evaluated. We use weighted peak signal to noise ratio for measuring image quality of watermarked images. Experimental results show that the proposed method outperforms the existing hybrid watermarking techniques.