A recent survey of self-embedding fragile watermarking scheme for image authentication with recovery capability <s> Experimental evaluation <s> Abstract The original hierarchical watermarking scheme for image tamper detection and recovery has simple computation and high performance precision which can achieve 2 × 2 subblock. However, four-scanning and blind attacks have been proposed recently on this scheme. We generalize these attacks and analyze the cause of security flaws. We think that it is promising to improve the original scheme's security and keep its merit at the same time. In order to defeat these attacks, we develop an improved method to generate a block mapping sequence by sorting the chaotic sequence and add the chaotic encryption and permutation based on the exact content of each subblock to be the post-processing of the 3-tuple watermark. Our method uses the simple watermarking scheme and satisfies the performance requirements of fragile watermarking, such as high-precision tamper detection, localization and recovery. Theoretical analysis and computer simulation demonstrate that our proposed scheme is much more secure and can overcome possible attacks. <s> BIB001 </s> A recent survey of self-embedding fragile watermarking scheme for image authentication with recovery capability <s> Experimental evaluation <s> A novel self-embedding watermarking scheme for tampering recovery is proposed. Two types of modes, i.e., overlapping and overlapping-free embedding, are used. Flexible, MSB-based, interleaved reference bits are embedded for content recovery. Embedding modes can be adaptively chosen to achieve optimal performances. Theoretical analysis and experiments are given to show the superiority of our scheme. In this paper, we propose a novel self-embedding fragile image watermarking scheme for tampering recovery based on reference-data interleaving mechanism and adaptive selection of embedding mode. During watermark embedding, reference bits are derived from the interleaved, scrambled MSB bits of original image, and then are combined with authentication bits to form the watermark bits for LSB embedding. Different with the reported schemes with the fixed embedding mode, the proposed scheme not only has two types of embedding modes, i.e., overlapping-free embedding and overlapping embedding, but also utilizes the adaptively flexible numbers of MSB and LSB layers to achieve satisfactory performances for different tampering rates. Also, detailed analyses are given to provide the theoretical values of watermarked-image quality, perfect recovery probability, and recovered-image quality, which are used to conclude the optimal choice of embedding modes. Experimental results show the effectiveness and superiority of the proposed scheme compared with some state-of-the-arts schemes. <s> BIB002 </s> A recent survey of self-embedding fragile watermarking scheme for image authentication with recovery capability <s> Experimental evaluation <s> DCT based effective self-recoverable fragile watermarking scheme is presented.This scheme has extreme localization and restoration capability.The blocking artifacts negligible because of using the small blocks of size 2×2.Two levels hierarchical tampered detection mechanisms are used for tampered block detection. This paper presents a Discrete Cosine Transformation (DCT) based effective self-recoverable fragile watermarking scheme. For each 2 × 2 non-overlapping block, two authentication bits, and ten recovery bits are generated from the five most significant bits (MSBs) of pixels. Authentication bits are embedded in the three least significant bits (LSBs) of the block itself while recovery bits are embedded in the three LSBs of the corresponding mapped block. The proposed watermarking scheme is also effective because the authentication of each block is based on two levels hierarchical tampered detection mechanisms. So the detection of tampered block can be ensured with high probability. The experimental results demonstrate that the proposed scheme not only outperforms high-quality restoration effectively, but also removes the blocking artifacts and improves the accuracy of tamper localization due to the use of very small size blocks, smoothing function and two levels tampering detection mechanisms. <s> BIB003
In this section, to clarify the process of watermark insertion, authentication and recovery, we conduct an experimental evaluation of four fragile watermarking techniques: Singh BIB002 , which used LSB method. A large number of test images sized 512 × 512 are used in our experiments to demonstrate the effectiveness of the schemes. We use three standard test images: Airplane, Lena and Baboon as shown in Fig. 12 . Lena is considered as low-textured, Airplane as medium From the block diagram for all of schemes, it can be underlined that there are three main phases that can be explained as follows: (1) watermark generation and insertion: in this phase, the results of imaging are generated from the host image. Furthermore, the authentication bits of each block are obtained from the slightly digested image. First, to improve safety, the permutation coefficient is used   . Then, all the coefficient bits embedded in each block are shuffled and encrypted using a specific key BIB003   BIB002 . Finally, the digest image and authentication bits are merged and embedded in the host image with the LSB technique. (2) Detection and authentication of tamper: after receiving a watermarked image, for authentication, first of all, the digested image and authentication bit are extracted. Then, based on the extracted data, the image is analysed to check the authenticity of manipulation and destruction. If the image contains damaged parts, the recovery phase tries to recover the original content. (3) Recovery and reconstruction: in the final stage, based on the mapped blocks, invalid blocking (damaged areas) is restored using image imagery embedded in the host. Furthermore, all the proposed fragile watermarking methods use non-overlapping image block sized 2 × 2, except the scheme proposed by Qin et al.  , which uses overlapping image block sized 3 × 3. The use of smaller blocks allows better detection and recovery processes. A larger block size will result in a more sensitive damage detection. For example, even if only one pixel in a 3 × 3 pixel block is damaged, then the entire block will be detected as a broken block, thus the recovery process is carried out in all areas of damage, and will be replaced with other values as a whole. Fig. 18 Example of the 20% tampered Airplane image with cropped image of four schemes. (a1-a4) Scheme BIB003 ; (b1-b4) scheme  ; (c1-c4) scheme  ; (d1-d4) scheme BIB002 . The block diagrams show a slight difference in the watermark embedding process, wherein Singh uses three LSB as the watermark insertion point, here it can be seen with three LSB that the additional information store capacity is 12 bits, 8 bit for recovery and 4 bit for authentication, while the other methods use two LSB, so it can only hold 8 bits, 6 bit for recovery and 2 bit for authentication. The advantage of using less LSB is in the result of the watermarked image that does not show any significant change, so the value of PSNR is also high, it can be seen in Fig. 17 . The PSNR value of the watermarked image decreases with the increase of watermark payload. As shown in Fig. 17 , the PSNR of the Singh et al.'s watermarked image was below the others because there were differences in the payload, where the watermark payload of Singh used 2 bpp and others used 3 bpp. The performance of the four methods may vary by type of distortion. In this paper, we compare those using cropping attacks with various error percentages. The cropped attack is done by removing some portions of the image into another size that the attacker wants. To describe this, Fig. 18 illustrates the example of localisation of destruction for 20% of tamper in the Airplane image and their recovered image. The rows in Fig. 18 show an example of the tamper detection and recovery process of four methods, which is the first to fourth column as original images, tampered images, tamper detection and tamper recovery, respectively. To compare the success of both methods in terms of image recovery, PSNR measurements were performed for three images in average using Eq. (1). PSNR is measured by comparison of recovered image to watermarked image. The obtained results for the four schemes can be seen in Fig. 19 . The PSNR result of Qin et al.'s method BIB002 reaches the highest value, followed by method BIB003   , because the insertion scheme proposed by Qin et al. BIB002 can be categorised into overlapping and non-overlapping, which are related to variable numbers from the MSB layer and the LSB layer used during watermark insertion. Based on the interleaving reference mechanism, MSB bits representing the contents of the block principle are inserted to produce reference bits, and then, are entered into LSBs. Because both the number of MSB layers and the LSB layer used affect the quality of the watermark image, affect the likelihood of complete recovery and the restored image quality, detailed analysis is given to provide the theoretical value and present optimal choice of embedding mode. To further test the precision of tamper detection, PFD written in Eq. (10) are employed in this paper BIB001 . Table 4 shows the results under cropped attack, which is similar to example illustration as shown in Fig. 17 . PFD is used to evaluate the tamper detection performance. The lower the PFD, the better the tamper detection performance is. Ideally, PFD of the watermarking scheme for authentication would be close to zero. It is seen that PFD of Qin et al.'s method is 0, in which all tampered blocks have been localised. Qin et al.'s results show the superiority compared with some state-of-the-art schemes, because the scheme utilises flexible numbers of the MSB layers to generate the interleaved reference bits for content recovery. They compare the recalculated authentication bits from the extracted authentication bits-if different, the block is judged as having been tampered. Otherwise, the block is marked as intact. Because the watermark concealment process for the detection process is inserted in the original block, it is possible that the comparison of block per block in the affected image with a watermarked image will be easily detected. So that for cropping attacks can be detected properly according to the location of the damage that has been raised.