## 2 Related Works
For each block of \(4\times 4\) pixels, 12 bits of authentication are generated, and for each block of \(2\times 2\) pixels, 20 bits are generated for the recovery process. The embedding scheme is based on the LSB method, where watermarks are embedded into the two LSB bits of each pixel. [PERSON] [23] proposed an improvement of the reconstruction scheme based on watermarking and the _set partitioning in hierarchical trees_ (SPIHT) transform, where this scheme uses blocks of \(32\times 32\) pixels to generate the reconstruction bits. Additionally, this algorithm incorporates two versions of the recovery bits to obtain better robustness against the tampering coincidence problem. This scheme's main disadvantage is that the SPIHT transform can result in wrong recovery bits extracted for a block. Therefore, a complete block can be recovered with inferior quality, resulting in poor objective quality of the reconstructed image. [PERSON] et al. [24] proposed a scheme based on the _integer wavelet transform_ (IWT), where the recovery and authentication bits are generated using this transformation, and the embedding scheme is based on LSB. This scheme does not embed the redundancy in data, and as a result, suffers the drawback that it cannot avoid the tampering coincidence problem. [PERSON] et al. [25] proposed a system based on a semi-fragile watermark in the _discrete wavelet transform_ (DWT) domain. The generation of watermarks is performed by DWT-DCT, where the _low frequency_ (LL) sub-band is obtained, followed by the application of DCT for non-overlapped blocks. Finally, a quantization step to get the self-recovery watermark is used. The authentication watermark is a binary watermark correlated with the LL sub-band of the first DWT decomposition level. This method's principal drawback is its low self-recovery rate because the embedding stage for the recovery bits is performed at the second decomposition level of the DWT in the middle-frequency sub-bands. In [26], a semi-fragile watermark was employed using the IWT domain, where self-recovery bit generation was performed utilizing _integer discrete cosine transformation_ (IDCT), Huffman coding and an error-correcting procedure based on the _Bose-Chaudhuri-Hocquenghem_ (BCH) encoder. The authentication bits were obtained using the exclusive addition operation between the LL frequency sub-band and a pseudo-random sequence. [PERSON] et al. [27] used a semi-fragile watermark employing the IWT, where the authentication bits are embedded in the LL sub-band; in the opposite, the self-recovery bits are embedded in the _high-low_ (HL) and _low-high_ (LH) frequency sub-bands. The self-recovery bits are generated by IWT, DCT and a quantization process to obtain the DCT coefficients. Additionally, the tamper detection bits are caused by a bitwise exclusive OR operation between a pseudo-random sequence and a binary matrix. In a recent study [36], we have proposed a novel method performed on an image in _luma and chroma_ (YCbCr) color space, implementing the halftoning algorithm in the luminance channels, thus obtaining recovery bits. Additionally, this scheme uses the procedure proposed in [15], where for chrominance channels, the watermark bits are also generated for recovery purposes. Additionally, three copies of these bits were embedded using the 2-LSB method, incrementing the robustness, and in such a way resolving the tampering coincidence problem. Contrarily, this study's proposition consists of the SR-HTR method, which uses a block-based method for the generation of recovery and authentication watermarks employing an RGB color image. The novel framework is designed in three variants (1-LSB, 2-LSB and 3-LSB), where for each variant, there can be embedded three, six and nine copies of the recovery watermark, respectively.