05-05-2011, 03:56 PM
Abstract:
Problem statement: In recent years, as digital media are gaining wider popularity, theirsecurity related issues are becoming greater concern. Method for authenticating and assuring theintegrity of the image is required. Image authentication is possible by embedding a layer of theauthentication signature into the digital image using a digital watermark. In some applications tamperlocalization is also required. Approach: In this study, we proposed a fragile image authenticationsystem with tamper localization in wavelet domain. In this scheme, secret data to be embedded is alogo. Watermark was generated by repeating logo image so that size of watermark matches with thesize of HH sub-band of integer wavelet transform. To provide additional level of security, thegenerated watermark was scrambled using a shared secret key. Integer Haar wavelet transform wasapplied to obtain wavelet coefficients. Watermark was embedded into the coefficients using odd-evenmapping.
Results: Experimental results demonstrated that proposed scheme detected and localizedtampering at pixel level. Proposed scheme was tested with images of various sizes and tampering ofvarious sizes. It provided good results for tamperings ranges from single pixel to a block of pixels.
Conclusion: Watermarking was done in wavelet domain; conventional watermarking attacks were notpossible. The resolution of tamper localization was achieved at pixel level. The watermarked image’squality was still maintained while providing pixel-level tampering accuracy. Proposed scheme can beused in insurance, forensics departments.
Key words: Watermarking, authentication, tamper localization, integer wavelet transform
INTRODUCTION
In recent years, as digital media are gaining widerpopularity, their security related issues are becominggreater concern. Digital watermarking is a techniquewhich allows an individual to add copyright notices orother verification messages to digital media. Imageauthentication is one of the applications of digitalwatermarking, which is used for authenticating thedigital images. The objective is not to protect thecontents from being copied or stolen, but is to providea method to authenticate the image and assure theintegrity of the image. The way to realize this featureis to embed a layer of the authentication signature intothe digital image using a digital watermark. In the caseof the image being tampered, it can easily be detectedas the pixel values of the embedded data wouldchange and do not match with the original pixelvalues[1]. There are many spatial and frequencydomain techniques available for authenticationwatermarking[2-8].In message authentication, only the image integrityis verified, but sometimes this is not sufficient in digitalimages and tamper localization is also required. Thesituations include forensics, crime, insurance. Tamperlocalization is used to identify the specific positionswhere the tamper has occurred.To achieve tamper localization many existingschemes use block-based approach[9-12]. One of the firstfragile watermarking techniques proposed fordetection of image tampering was based on computingcheck-sums of gray levels which is determined fromthe seven most significant bits of the image. Thecheck-sum is embedded into the Least Significant Bits(LSBs) of pseudo-randomly selected pixels[9]. Oneweakness of this scheme is that it is possible to swapblocks in an image without causing a detectablechange. It is called as Vector-Quantization (VQ)attack or transplantation attack. But, VQ attack can beavoided by including the block position or block indexto the image data before hashing[10]. The watermarkcan be calculated in a multi level hierarchy so thatboth VQ attack resiliency and high accuracy fortampering localization is achieved[11]. The watermarkmay include not only the block location but also acontent-feature of another block and a CyclicRedundancy Check (CRC) checksum[12]. The CRCchecksum is used to authenticate the block inspectedwhere as the block location and content-feature ofanother block are used for complicating
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Problem statement: In recent years, as digital media are gaining wider popularity, theirsecurity related issues are becoming greater concern. Method for authenticating and assuring theintegrity of the image is required. Image authentication is possible by embedding a layer of theauthentication signature into the digital image using a digital watermark. In some applications tamperlocalization is also required. Approach: In this study, we proposed a fragile image authenticationsystem with tamper localization in wavelet domain. In this scheme, secret data to be embedded is alogo. Watermark was generated by repeating logo image so that size of watermark matches with thesize of HH sub-band of integer wavelet transform. To provide additional level of security, thegenerated watermark was scrambled using a shared secret key. Integer Haar wavelet transform wasapplied to obtain wavelet coefficients. Watermark was embedded into the coefficients using odd-evenmapping.
Results: Experimental results demonstrated that proposed scheme detected and localizedtampering at pixel level. Proposed scheme was tested with images of various sizes and tampering ofvarious sizes. It provided good results for tamperings ranges from single pixel to a block of pixels.
Conclusion: Watermarking was done in wavelet domain; conventional watermarking attacks were notpossible. The resolution of tamper localization was achieved at pixel level. The watermarked image’squality was still maintained while providing pixel-level tampering accuracy. Proposed scheme can beused in insurance, forensics departments.
Key words: Watermarking, authentication, tamper localization, integer wavelet transform
INTRODUCTION
In recent years, as digital media are gaining widerpopularity, their security related issues are becominggreater concern. Digital watermarking is a techniquewhich allows an individual to add copyright notices orother verification messages to digital media. Imageauthentication is one of the applications of digitalwatermarking, which is used for authenticating thedigital images. The objective is not to protect thecontents from being copied or stolen, but is to providea method to authenticate the image and assure theintegrity of the image. The way to realize this featureis to embed a layer of the authentication signature intothe digital image using a digital watermark. In the caseof the image being tampered, it can easily be detectedas the pixel values of the embedded data wouldchange and do not match with the original pixelvalues[1]. There are many spatial and frequencydomain techniques available for authenticationwatermarking[2-8].In message authentication, only the image integrityis verified, but sometimes this is not sufficient in digitalimages and tamper localization is also required. Thesituations include forensics, crime, insurance. Tamperlocalization is used to identify the specific positionswhere the tamper has occurred.To achieve tamper localization many existingschemes use block-based approach[9-12]. One of the firstfragile watermarking techniques proposed fordetection of image tampering was based on computingcheck-sums of gray levels which is determined fromthe seven most significant bits of the image. Thecheck-sum is embedded into the Least Significant Bits(LSBs) of pseudo-randomly selected pixels[9]. Oneweakness of this scheme is that it is possible to swapblocks in an image without causing a detectablechange. It is called as Vector-Quantization (VQ)attack or transplantation attack. But, VQ attack can beavoided by including the block position or block indexto the image data before hashing[10]. The watermarkcan be calculated in a multi level hierarchy so thatboth VQ attack resiliency and high accuracy fortampering localization is achieved[11]. The watermarkmay include not only the block location but also acontent-feature of another block and a CyclicRedundancy Check (CRC) checksum[12]. The CRCchecksum is used to authenticate the block inspectedwhere as the block location and content-feature ofanother block are used for complicating
Download full report
http://www.scipubfulltext/jcs/jcs511831-837.pdf