In recent years, digital watermarking technique has become the most useful method for protecting the ownership of a user's digital content, and it can be used to verify ownership by embedding a user's digital watermark into that digital content. By showing the watermark, someone can prove legal ownership of the intelligent property on the digital content. Because of the maturity of e-commerce on the Internet, users can purchase digital content through buyer-seller watermarking protocols, and these protocols can help users to embed their watermarks into their digital content. After the transaction is terminated, users can also obtain their own digital content with the desired watermark embedded. However, when users attempt to exchange their digital content with each other over a network, it is important that a secure and efficient method be used. If users directly execute one of the above buyer-seller watermarking protocols, they will find that it cannot achieve significant transfers of digital content. On the other hand, they cannot be guaranteed that the transaction will be fair and efficient. Besides, when users are located on different networks, it is important to understand how they can obtain a protocol that is fair and efficient. To address these problems, we propose efficient and fair digital content exchange protocols for different networks such as Ethernets, P2P networks and cloud networks. Our proposed protocols can achieve identity authentication before performing the digital content exchange protocol, and can also maintain fair transactions between users. Finally, we also provide the formal security proofs for the proposed protocols and properties comparisons with other related schemes. Moreover, our protocols also offer solutions that are suitable for users who are located on different networks, and guarantee that digital content exchange transactions will be performed fairly and efficiently.