Abstract
A novel iris biometric watermarking scheme is proposed focusing on iris recognition instead of the traditional watermark for increasing the security of the digital products. The preprocess of iris image is to be done firstly, which generates the iris biometric template from person's eye images. And then the templates are to be on discrete cosine transform; the value of the discrete cosine is encoded to BCH error control coding. The host image is divided into four areas equally correspondingly. The BCH codes are embedded in the singular values of each host image's coefficients which are obtained through discrete cosine transform (DCT). Numerical results reveal that proposed method can extract the watermark effectively and illustrate its security and robustness.
1. Introduction
With the internet age coming, amount of digital products have swarmed into our living. Especially the digital products are inevitable for being copy-free. Therefore, the security of these products is presented over the past few decades. A typical solution is the digital watermarking technology which has been widely applied to information security, such as copyright protection and authentication. Watermarking can be classified into visible and invisible. Visible watermarking is attacked even more than invisible because visible watermarking is disclosed [1]. In contrast, invisible watermarking is more prevalent. Invisible watermarking could be done in the spatial domain or in the transform domain according to human visual system (HVS). However, transform-domain-based watermarking techniques present advantages in terms of perceptibility and robustness more than the spatial domain, so more researchers pay attention to the transform domain. Researchers frequently used the transform domain including the Fourier transform, discrete cosine transform (DCT), discrete wavelet transform (DWT), and many more.
In biometrics feature recognition, iris has become focus and emphasis which has unique, stability, be-collected, non-invasion, and so forth as an important characteristic of authentication. Daugman has made many contributions to iris-based biometrics [2, 3]. Wildes et al. have proposed an automated iris recognition [4]. Wildes et al. [4, 5], Boles and Boashash [6] have obtained some research on the iris recognition. More and more research institutes and companies have been added to the field of iris recognition [7, 8]; iris-based authentication technology is paid attention to by academia and business. A lot of standard databases have been generated by various institutes to work in this field [9, 10]. Lots of organizations are focusing on the issue, such as Chinese Academy of Sciences-Institute of Automation (CASIA) [11], Lion’s Eye Institute (LEI) [12], Universities of Bath, and Carnegie Mellon University, and we use the database from University of Bath. Similar method is discussed in [13–20].
To sum up, we focus on the iris biometric database, a novel iris biometric watermarking based on singular value decomposition (SVD), and DCT is proposed.
The preprocess of iris image is to be done firstly, which generates the iris biometric template from person’s eye images. And then the templates are to be on discrete cosine transform; the value of the discrete cosine is converted to BCH-based coding. The host image is divided into four areas equally correspondingly. The DCT coefficients of each area are applied with the SVD [21, 22]. The DCT coefficients of each area are modified by the singular vectors and the BCH-based error control coding watermark to embed the watermark image. Embedding intensities depends on the key. The algorithm is robust under popular attacks.
2. Iris Image Technology Normalization and Coding
We use the database of eye images from University of Bath. In addition to iris, there are pupil, sclera, and eyelid in any eye image. It is necessary to normalize to remove these adverse factors from eye image prior to coding. We apply a minimum bounded isothetic rectangle (MBIR) format to eye image for eliminating these factors. Thus, we obtain rectangular iris templates which are normalized to a size of pixels by MBIR format [23, 24]. The normalized iris image is applied with column-wise, 1D DCT and retaining of DC value of each column, to obtain a set of pixels [23, 25, 26]. Then, these DC values are encoded to binary string, which is bits format with BCH-based error control coding (Figure 1).
3. Watermarking Methodology
Discrete cosine transform is correlated with Fourier transform, which is similar to the discrete Fourier transform and only use real parts. 2D DCT transformation is commonly used in video compression conversion. In the compression process, the image is divided into many small pieces of format. A signal is converted into frequency domain as follows: where . Then the watermark-embedding process is discussed in the following steps.
Step 1. The host image is divided into four blocks equally , which block is applied with DCT , .
is an important matrix factorization in linear algebra which has some important application in signal processing, statistics, and other fields.
Suppose is a matrix, the elements of which all belong to domain, that is, real domain or complex domain. Thus, it exists a decomposition such that:
where is unitary matrix and is the conjugate transpose of which also is unitary matrix. We choose special orthonormal bases: for the row space and for the column space. is positive semidefinite matrix of and is the singular value of :
Step 2. is implemented by SVD for each block:
Step 3. Iris image is normalized and encoded to binary string. Here iris image is converted to bits binary, which is divided into four sections equally and each section is 400 bits binary. The 400 bits binary change into 403 bits added with 3 zero values at the end of the 400 bits. The 403 bits binary is converted to BCH(511,403), where , , and . The watermark consists of these four sections.
Step 4. Watermark is embedded into the singular values of the DCT-transformed host image on each block:
Step 5. The DCT coefficients of watermarked image are modified in each block:
Step 6. The watermarked image is performed inverse DCT (IDCT) on .
For illustrating the watermark embedded process, the description figure is presented as shown in Figure 2.
For the watermark-extraction process, we consider that the received image is corrupted version of the watermarked image. And the description of the watermark extraction process is presented in Figure 3.
Step 1. In this step of the extraction process, the corrupted image is divided into four areas equally.
Step 2. is applied with DCT:
Step 3. SVD operation is implemented on :
Step 4. Watermark is hidden in the singular value of , so watermark is expressed by the following:
Step 5. is divided into four sections equally; then, each section is processed error correction decoding, as is binary BCH coding. The result of the decoding is that is 1600 bits binary format.
Step 6. Perform mod 2 operation on : where , , , and is vector.
Step 7. Do a summation of the elements in :
Step 8. Take the minimum of as :
Step 9. This is done conversion of the binary format into the DC values.
Step 10. The obtained set of DC coefficients is contrasted with the standard sets of DC coefficients stored for each person and judged to belong to who in the database.
4. Experiment Results and Discussion
Because the iris biometric has the superiority of security, imperceptibility, the iris biometric is employed to realize embed watermark. Via the conclusions discussed in [27], the DC coefficients of different persons’ iris, which can be seen to be noncorrelated, has a non-self-similar characteristic as shown in [27]. However, the variation of DC coefficients of the same iris biometric has a self-similar characteristic as in [27] in diversification condition. In terms of iris characteristics, the DC coefficients of iris biometric are used as a watermark.
The detected watermark is a binary string in our proposed scheme, so the detected watermark is divided into two types of situation. One type of situation is that the detected watermark could match up with someone’s iris biometric in the database, so it is the identification of the biometric. The embedded watermark and the detected watermark belong to the same iris, that is, correct detection, or the embedded watermark and the detected watermark do not belong to the same iris, that is, false acceptance. Another type of situation is that the detected watermark could not match up with anyone’s iris biometric in the database, so it is false rejection. In the above types, we only pay attention to correct detection, for it is significant to identify the detected watermark. According to Figures 1–3, the proposed scheme and the algorithm [23] are all viewed as digital communication system, it has greatly raised the correct-detection probability. Thus it is hard to measure the performance by traditional methods such as PSNR and ROC curve, it can be to measure the performance by the algorithm [23].
In [27], there are 77 different attacks. In their results of experiment, both the identification 67 of the 77 attacks which has greater than 90% of correct detection and the identification 71 of the 77 attacks which has greater than 85% of correct detection have been successful. This algorithm [27] displays robustness when receiving most attacks by detection and identification except the “copy” attack. Some attacks like “scaling,” “MAP,” “up-down sampling,” and “bending” attacks are partially sustained. In this paper, the proposed algorithm almost has a good performance with the different attacks. There are 70 different attacks; the identification 60 of the 70 attacks which has greater than 95% of correct detection, the identification 61 of the 70 attacks which has greater than 90% of correct detection, and the identification 66 of the 70 attacks which has greater than 85% of correct detection have been successful, all shown in Table 1.
5. Conclusion
In this paper, the DC coefficients of the same iris biometric have a self-similar characteristic to reduce complexity of implementation. BCH(511,403) codes have a 12 bits error-correction function. It has largely improved the correct-detection probability of extracted watermark in comparison with traditional watermark. Furthermore, four extracted watermarks are compared one by one so that the best one can be selected. This process also improves the correct-detection probability. A series of experiments have been conducted to validate the performance of the proposed SVD and DCT. The experimental results show that the proposed scheme has a more superior performance than the other methods under different kinds of attacks. The proposed algorithm based on SVD and DCT has robustness and imperceptibility.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgment
This present work was supported partially by the Polish-Norwegian Research Programme (Project no. Pol-Nor/200957/47/2013). The authors highly appreciate the above financial supports.