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.     

实用的完全脆弱认证水印算法*

提出一种完全脆弱认证水印算法用于图像完整性认证、窜改定位和近似恢复被窜改部分。算法基于对原始图像2×2大小分块,计算图像块各像素高6 bit的灰度均值作为水印,利用混沌和置乱技术对水印信息进行加密和确定水印比特嵌入的位置。实验结果表明,该算法简单、安全性高,窜改精确定位到2×2图像块,可对窜改区域近似恢复,具有较好的实用性。     

一种基于安全隐藏的图像分层窜改检测和内容恢复算法

提出了一种可用于数字图像的分层窜改检测和内容恢复的脆弱水印算法。图像中每个分块产生的水印信息包括认证水印和内容恢复水印,其中认证水印由奇偶校验和平均强度信息生成,恢复水印由分块DCT系数量化编码后的信息得到。根据混沌映射和最远距离安全隐藏机制,将恢复水印嵌入到映射块中,可有效避免窜改一致性问题。在接收端,采用分层窜改检测方法,减少窜改分块的漏判和误判,有效提高了窜改精度和恢复质量。实验结果表明,提出的方法与已有方法相比,无论在小面积窜改或大面积窜改情况下均可取得较好的恢复效果。     

块截断编码的图像自嵌入半脆弱水印算法

目的 数字图像自嵌入水印技术是解决图像篡改检测和恢复问题的主要技术手段之一,现有的自嵌入水印技术存在着认证粒度不高、嵌入水印后的图像失真较大,且无法抵抗滤波等操作。为提高图像自嵌入水印的认证粒度以及抵抗滤波等处理操作的能力,提出了一种基于块截断编码的图像自嵌入半脆弱水印算法。方法 水印生成与嵌入：首先,将图像进行块级别的二级划分,分别生成粒度为4×4和2×2的图像块;然后,利用块截断编码对每个4×4图像块进行压缩编码,生成2×2图像块的恢复水印,并对恢复水印进行哈希生成2×2图像块的认证水印;最后,将恢复水印和认证水印级联构成自嵌入水印,嵌入到映射块中。篡改认证与恢复：首先,将某个4×4图像块提取的水印与该块生成的水印比较,判别该图像块的2×2子块是否通过认证;最后,依据认证结果对2×2图像块实施恢复。结果 该算法产生的水印图像的峰值信噪比（peak signal-to-noise ratio,PSNR）均高于44 dB,在50%的篡改率下,恢复后的图像质量可达到32.7 dB。该算法生成水印并在图像上嵌入大约需要3.15 s,恢复图像大约需要3.6 s。结论 算法利用块截断编码,有效缩短了生成的水印长度,保证嵌入水印后图像的质量。此外,通过引入的可容忍修改阈值,使得水印能够对滤波等图像处理操作具有一定的鲁棒性,同时保证对图像的恶意篡改具有敏感性。最后通过与最近典型方法的对比实验,验证了算法在嵌入水印后图像质量、恢复图像质量等方面的优势。     

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。     

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.     

用于图像认证的小波域双重脆弱水印算法研究

针对当前小波域脆弱水印图像认证算法不能有效抵抗矢量量化攻击以及虚警率和漏警率较高的问题,基于混沌理论和块相关策略,提出一种小波域双重脆弱水印图像认证算法。算法首先对载体图像分块并建立块相关映射表;再对每一图像块作一级整数提升小波变换,利用Logestic混沌系统生成基于近似子带LL特征的水印信号;最后将水印信号分别嵌入相关图像块的细节子带HL和LH。实验结果表明,该算法不仅能很好地抵抗矢量量化攻击,而且具有较低的虚警率和漏警率,能很好地实现图像完整性认证功能。     

用于图像认证的小波域双重脆弱水印算法研究

针对当前小波域脆弱水印图像认证算法不能有效抵抗矢量量化攻击以及虚警率和漏警率较高的问题,基于混沌理论和块相关策略,提出一种小波域双重脆弱水印图像认证算法.算法首先对载体图像分块并建立块相关映射表;再对每一图像块作一级整数提升小波变换,利用 Logestic 混沌系统生成基于近似子带 LL 特征的水印信号;最后将水印信号分别嵌入相关图像块的细节子带 HL 和 LH.实验结果表明,该算法不仅能很好地抵抗矢量量化攻击,而且具有较低的虚警率和漏警率,能很好地实现图像完整性认证功能.     

一种自嵌入的图像脆弱水印算法

针对现有脆弱水印算法大多无法区分水印被篡改还是内容被篡改的问题,提出了一种基于奇异值分解的自嵌入水印算法.算法基于原始图像2×2大小分块,图像块的高6位进行奇异值分解,每块的最大奇异值经过量化生成恢复水印嵌入到偏移子块的次低位,每块的奇异值范数二值编码生成认证水印嵌入到本身的最低位.实验结果表明,该算法不仅篡改定位准确,而且能区分是水印被篡改还是图像内容被篡改,可有效地恢复被篡改的区域.     

一种基于分块DCT的混沌半脆弱图像水印技术*

提出了一种用于数字图像内容认证的半脆弱水印方案。将图像进行分块,图像块的归一化标准差经量化操作后映射为混沌系统初值,经混沌映射生成水印比特。用量化系数技术将水印比特嵌入块DCT直流系数。利用混沌对初值极端敏感性的特点,能够定位检测对加入水印图像的窜改,并且水印提取不需要原始图像。实验结果表明,嵌入水印后图像的视觉质量好;算法具有对图像内容局部窜改检测的有效性、敏感性以及良好的窜改定位能力,并具有更好的抗JPEG压缩、加性高斯噪声和中值滤波的鲁棒性。     

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.     

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.     

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.     

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。     

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)     

对水印信息篡改鲁棒的自嵌入水印算法

为提高自嵌入水印算法在任意篡改条件下的篡改恢复质量,提出一种对水印信息篡改鲁棒性的空域自嵌入水印算法,分析了算法中阈值选取的合理性和检测篡改的可靠性.该算法首先基于密钥将原始图像的最低位和1/4次低位置零,通过对图像内容的小波低频系数实施均匀标量量化生成低频特征图像,将低频特征图像置乱加密后生成的二值编码嵌入原始图像的置零位;认证时通过设定的阈值识别图像内容被恶意篡改的图像块,从而提高自嵌入水印算法对水印信息篡改和信道噪声的鲁棒性.理论分析和仿真结果表明,无论水印信息被随机篡改还是区域篡改,算法均能根据阈值区分不同篡改并选用不同的方法对其进行篡改恢复,有效地提高了自嵌入算法在部分水印信息篡改时的恢复质量.     

一种基于自适应量化的半脆弱图像水印算法

提出了一种基于自适应量化的半脆弱图像水印嵌入方案，能够在不参考原始载体的情况下对数字图像同时进行版权保护和内容认证．该半脆弱水印嵌入方案具有以下特点：（1）抽取并利用了原数字水印的特征信息（作为辅助水印）；（2）采纳了基于人眼视觉特性的自适应量化策略；（3）数字水印信息的提取不需要原始载体图像；（4）采用整型提升小波变换，克服了小波域水印算法普遍存在的舍入误差问题；（5）能够同时进行版权保护与内容认证，并可确定篡改发生区域．仿真实验表明：该小波域水印嵌入方案不仅对JPEG压缩、叠加噪声、平滑滤波等常规图像处理具有较好鲁棒性。而且能够对替换等恶意图像篡改做出报警反应，同时其误检率与漏检率等关键技术指标均优于现有半脆弱水印嵌入算法．     

Block-based fuzzy-image authentication method

Abstract

Fragile watermarking methods have been widely used for image authentication. A novel image-authentication method based on fuzzy coding is presented in this work. This method is a block-based method and it consists of watermark generation, watermark embedding, watermark extraction, tamper detection, and image recovery phases. First, the cover image is divided into nonoverlapping blocks. In the watermark-generation step, fuzzy sets and fuzzy coding are used. To generate fuzzy sets, three threshold points are selected from a histogram of the cover image and fuzzy sets are created by using these threshold points. Memberships of pixels are calculated to generate features. Fuzzy coding is used to generate the watermark. The watermark-embedding function uses ±1 data hiding function for each block. Therefore, high visual quality is achieved. The generated watermark is compared with the extracted watermark in the tamper-detection phase. Finally, a new image-recovery algorithm is proposed for recovering tampered areas. To evaluate the proposed method, visual quality, tamper detection ability, image recovery capability, and computational complexity were used. The experimental results clearly indicated that the proposed method was a success.