# Secure Watermarking Schemes and Their Approaches in the IoT Technology: An Overview
## 4 Related Research: Modified Watermarking Approaches in the IoT Applications
### Fragile  
The researchers in [104; 105] produce a number of chained fragile watermarks that aim to reduce the computational overhead and to detect unauthorized modification attacks. This technique starts by dividing the WSN data into a number of fixed size groups. Following that, the hash function is used to associate the group data along with the key and group serial numbers. The output of the hash function is used to generate the watermarked segment in each group. Finally, the watermarked segment is warehoused in the former group as a linked list model. The proposal experiments show the improvement in reducing the computational overhead, which reflects on the WSN's lifetime.  
The researchers in [16] propose a fragile watermarking technique in order to maintain data integrity among the three IoT layers. In fact, this technique relies on computing the hash value for data, which are collected by the WSN in the perception layer. After that, a random location-based watermark approach is applied to compute the embedding position. Finally, the watermarked object is sent to the network layer. This technique contributes to secure data blocks from different attacks such as forwarding, tampering, replaying and spoofing. In [106], the researchers propose a lightweight fragile watermarking technique for improving the data integrity among the communication WSN nodes. This algorithm is based on the use of the MAC address node and hash function along with the embedding scheme.  
Furthermore, the researchers in [107] produce a semi fragile watermarking method for recovery and attack detection. It mainly uses the IWT and DCT for identifying malicious attacks and recovery where it mainly focuses on enhancing the Enterprise Multimedia Security mechanism. To implement the tamper detection and recovery purposes, two different types of watermarking techniques are generated, which comprise: the recovery watermark and the authentication watermark. The embedding method of the proposed watermarking generation creates an acceptable PSNR of the watermarked images. Additionally, the proposed tamper detection mechanism is tested against various types of content preserving manipulations. These types include the addition of salt, speckle and pepper noise, wiener filtering, scaling, geometric attacks, gamma correction, image brightening and blurring. The findings show a correctly verified image authenticity.  
In [61], the researchers propose a self-embedding authentication process in watermarking technology in order to discover and recover different tampered locations. Two types of detection processes are proposed, which comprise the pixel-wise and block-wise processes. In the pixel-wise process, the authentication data are created per pixel while it is created per block in the block-wise process. Therefore, the length of authentication data in the block-wise process is attuned according to the size of each block. Moreover, the two processes use six 512_512 grayscale images in order to validate their methodology, and they produced results that show better performance on the tamper discovery and image recovery within various heavily tampered images.