# Blockchain-Based Multimedia Content Protection: Review and Open Challenges
## 3 State-of-The-Art of Blockchain-Based Content Protection Systems
### Comparative Analysis  
This section presents a comparison and a fine-grained analysis of blockchain-based multimedia content protection schemes presented in Section 3 w.r.t. the attributes defined in the taxonomy (Section 2). The analysis is presented in the form of Tables 1 and 2, Figure 2, and an in-depth discussion on the systems' properties. The tables also allow a side-by-side comparison of the systems presented in Section 3. Table 1 presents the comparison of the schemes w.r.t. types of blockchain, transaction types, data automation, cryptocurrency, consensus protocols, and content protection techniques, while Table 2 compares the performance of these scheme w.r.t. the performance evaluation metrics mentioned in Section 2.7. In Tables 1 and 2, a cell contains \"-\" when the corresponding attribute is not addressed by the scheme. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**References** & **Types of Content** & **Types of Blockchain** & **Types of Transaction** & **Data Automation** & **Crypto-currency** & **Consensus Protocols** & **Content Protection Techniques** \\ \hline [PERSON] et al. & HD & & & & & & \\ (2015) [39] & video & Permissioned On-chain & – & Bitcoin & PoW & DRM \\ \hline [PERSON] \& [PERSON] & & & & & & \\ (2017) [44] & Image & – & On-chain & \begin{tabular}{c} Smart contract \\ \end{tabular} & Ethereum & – & Watermarking \\ \hline [PERSON] \& [PERSON] & – & Permissioned & Hybrid & dApp & Ethereum & – & Encryption \\ (2018) [36] & Audio & Permissionless & Hybrid & dApp & Ethereum & PoW & Watermarking-based DRM \\ \hline [PERSON] et al. & Video & Consortium & On-chain & dApp & \begin{tabular}{c} Ethereum \\ Token \\ \end{tabular} & PoW/PoS/ PBFT & DRM \\ \hline [PERSON] et al. & Video & Permissioned & Hybrid & dApp & Ethereum & PoW/PoS/ PBFT & Watermarking-based DRM \\ \hline [PERSON] et al. & Video & Permissioned & Hybrid & \begin{tabular}{c} Smart contract \\ \end{tabular} & Bitcoin & – & Watermarking \\ (2018) [46] & Image & Permissionless & Hybrid & – & – & – & Watermarking \\ \hline [PERSON] et al. & & & & & & & \\ (2019) [37] & Image & Permissioned & Hybrid & dApp & Ethereum & – & Encryption+Watermarking \\ \hline [PERSON] et al. & & & & & & & \\ (2019) [43] & Image & Consortium & On-chain & dApp & – & – & DRM \\ \hline [PERSON] et al. & & & & & & & \\ (2019) [45] & Document & – & Hybrid & \begin{tabular}{c} Smart contract \\ \end{tabular} & Bitcoin & – & Watermarking \\ \hline [PERSON] & & & & & & & \\ (2019) [48] & – & Consortium & Hybrid & \begin{tabular}{c} Smart contract \\ \end{tabular} & Ethereum & \begin{tabular}{c} Proof-of- \\ Authority \\ \end{tabular} & \begin{tabular}{c} Watermarking- \\ based DRM \\ \end{tabular} \\ \hline [PERSON] et al. & & & & & & & \\ (2019) [49] & – & Permissioned & On-chain & dApp & Ethereum & PBFT & Watermarking-based DRM \\ \hline [PERSON] et al. & & & & & & \\ (2019) [50] & Image & – & Hybrid & dApp & – & – & Fingerprinting \\ \hline [PERSON] \& Megias & Image, Audio, & & & & & \\ (2019) [51] & Video & Permissioned & Hybrid & \begin{tabular}{c} Smart contract \\ \end{tabular} & Ethereum & – & Fingerprinting \\ \hline [PERSON] et al. & & & & & & & \\ (2020) [38] & Document & \begin{tabular}{c} Self- \\ developed \\ \end{tabular} & Hybrid & – & \begin{tabular}{c} Customized coin \\ \end{tabular} & PoW & \begin{tabular}{c} ECC- \\ based encryption \\ \end{tabular} \\ \hline [PERSON] (2020) [52] & Image & – & On-chain & – & – & – & Encryption+ \\ \hline [PERSON] (2020) [53] & Audio & Permissionless & On-chain & \
\begin{tabular}{c} Smart contract \\ \end{tabular} & – & – &
\begin{tabular}{c} Content- \\ based Fingerprinting \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of blockchain-based copyright protection schemes with reference to the taxonomy. Figure 2: Analysis of security objectives of multimedia content protection techniques achieved by the analyzed systems.