Watermarking based image authentication and tamper detection algorithm using vector quantization approach

Abstract

In the present work, a novel image watermarking algorithm using vector quantization (VQ) approach is presented for digital image authentication. Watermarks are embedded in two successive stages for image integrity verification and authentication. In the first stage, a key based approach is used to embed robust zero level watermark using properties of indices of vector quantized image. In the second stage, semifragile watermark is embedded by using modified index key based (MIKB) method. Random keys are used to improve the integrity and security of the designed system. Further, to classify an attack quantitatively as acceptable or as a malicious attack, pixel neighbourhood clustering approach is introduced. Proposed approach is evaluated on 250 standard test images using performance measures such as peak signal to noise ratio (PSNR) and normalized hamming similarity (NHS). The experimental results shows that propose approach achieve average false positive rate 0.00024 and the average false negative rate 0.0012. Further, the average PSNR and tamper detection/localization accuracy of watermarked image is 42 dB and 99.8% respectively; while tamper localization sensitivity is very high. The proposed model is found to be robust to common content preserving attacks while fragile to content altering attacks.

Introduction

With development of the digital technology recreation of digitally generated information has become very easy, and can be transmitted by digital media with ease among other medias of message conveyance images are most common. Therefore protection of these images and its content authentication is important. To authenticate the integrity and authenticity of a digital image, digital watermarking techniques have been considered an effective technique [1], [2], [3], [4], [5]. The watermarking technique for authentication purpose can be classified as robust, fragile and semifragile watermarking techniques based on their level of security. A robust watermark finds application in the area of ownership verification and copyright protection [6], [7], [8], [9]. A fragile watermark destroys itself even for small accidental or intentional changes [10], [11], [12]. On the other hand, semi-fragile watermarking is a practical technique which can protect integrity of digital images and can locate the tampered areas [13], [14], [15], [16]. Thus fragile or semi-fragile watermarking are those image watermarking techniques which find application in images and video content authentication and tamper detection [7], [13], [16], [17]. Given the limitations of robust and fragile watermarking schemes, multiple-watermarking is applied to digital data where copyright protection and content authentication is required to be addressed simultaneously [7]. Lu [7], pioneered the concept of VQ based image watermarking technique. Various VQ (vector quantization) based watermarking techniques are recommended by researchers in the past decade for image watermarking [17], [18], [19], [20] with the objective of image compression and authentication.

Most of the methods suggested in above literatures need improvement in issues related to watermarked image quality, identification of attacks as malicious or content preserving manipulation, and efficiency of the system in authentication of images. Therefore, an efficient image authentication algorithm having a good visual quality of watermarked image, having the advantage of comparatively less bandwidth and storage space, with high accuracy in attacks classification, tolerant to acceptable manipulations, and high tamper detection accuracy needs to be designed. Thus in proposed work, watermarks are embedded in two successive stages. In the first phase robust watermark is used for “zero level watermarking” [21] utilizing the statistical properties of VQ indices for enhancing the security of watermarked image by biometric verification. The advantage of first stage of watermarking is, it does not affect VQ reconstructed image. In the second step, the semifragile watermark is embedded by using a Modified Index Key based method (MIKB) for image authentication. A “quantitative threshold-based approach” is suggested for classifying attacks and localizing tampered area. Further statistical analysis is done to find false positive rate, false negative rate, percentage of correctly identified authenticated images and percentage of falsely verified images to validate the correctness of the system. Thus, proposed image authentication method fulfils desired characteristics of an effective image authentication technique. The significant features of proposed improvised scheme are-

• Watermarks are embedded using VQ indices properties; it enhances security and saves bandwidth requirements.

• Random keys are used for embedding robust zero level watermark and semi-fragile watermark respectively; random nature of key improves the integrity and security of designed system.

• A quantitative analysis is suggested to classify the attack as malicious or content preserving attack.

• Tamper detection accuracy of proposed system is very high; it can detect tampering up to 10% as malicious attack.

• Biometric verification watermark is used to enhance reliability of designed system.

The structure of the paper is organized into three sections namely proposed scheme, Experimental results and discussion of deigned algorithm, and lastly conclusion of the paper is addressed.