## 2 Related Work
Although their study succeeded in detecting and localizing changes and image restoration to some extent, the method constitutes exact authentication and is sensitive to innocent changes, such as Lossy compression. [PERSON] et al. in [25] proposed a semi-fragile watermarking method in which two watermarks were embedded in a host image, one binary image watermark being embedded in the LL3 band of the third level DWT of the host image, the other watermark calculated as an image digest by taking the DCT of the DWT LL1 band and embedding the image digest into the LH2 and HL2 DWT bands. The first watermark was used for authentication and the second image digest watermark was used for image restoration and tamper localization. The authors claimed that their method ensured authentication, recovery of the image and localization of tampered areas. [PERSON] et al. in [26] took a colour image into YCbCr colour space, then the DWT LL1 of the Y channel was divided into 8 \(\times\) 8 blocks; each block was quantized by a luminance quantization table and the quantized LL1 values replaced the HH1 band of the Y channel. After taking inverse DWT, a robust watermarked image was obtained, which was then taken to the RGB colour space. After that, the red, green and blue channels were watermarked by a fragile watermark. The fragile watermark was inserted into the pixel domain. A sequence of ones and zeros represented the watermark, which was converted to base 10 digits by a 3n-base formula containing a parameter \(n\). Each obtained digit was watermarked as a bit sequence to the LSBs of n pixel values of the corresponding colour channel. In their paper, [PERSON] and [PERSON] claim to have devised a method that embeds two watermarks into the host image, one for authentication, the other for restoration [27]. The authentication watermark was calculated from the DWT LL1 band of the host image. The LL1 band was divided into blocks, the blocks being grouped into two groups, namely A and B. The blocks were paired as one block from group A, and one block from group B. For each pair of blocks, the DCT of the blocks was taken and compared with the corresponding DCT value of the paired block; a value of 1 or 0 was calculated according to a '\(<\)' comparison. The majority bits of the comparison bit sequences were combined to form the authentication watermark. The authentication watermark was embedded into the HL2 and LH2 bands of the host image's DWT HL1 band. The HL2 and LH2 values were divided by or multiplied by \(\alpha\), depending on the bit value to be embedded. A recovery watermark was obtained by quantizing the LL3 values of the host image, which were then watermarked to the HL1 band's five LSBs. Although a recovery watermark was embedded, the recovery process was not reported in the experiments. It is easy to insert a similar watermarked block or block pairs from a known authenticated image into another image for forgery purposes [22]. Therefore, in any authentication type of watermarking, if the inserted watermark does not depend on the host image itself, then it is vulnerable to counterfeiting attacks. If the method is block-wise, the watermark must be calculated from one of the block pair and inserted into the other one in the pair. Block-pairing must depend on a key so that it cannot be predicted. [PERSON] et al. [28] proposed a convolutional-neural-network-based watermarking algorithm resistant against print-cam attacks, which are very strong attacks and introduce several distortions during picture capture. The proposed approach was compared with Fourier-transformation-based watermarking. The results obtained were robust, secure and of high quality. [PERSON] et al. [29] proposed a Chinese cryptographic algorithm for copyright protection. Nowadays, it is very easy to collect, share, distort, and change images and videos using information technology. It is a concern for everyone because of the security and copyright implications.