NFTs are virtual assets that represent digital or physical items such as art, music, in-game items and videos (underlying work). Such underlying work may be subject to copyright and authors rights(1) protection. A buyer may believe that by buying an NFT, they own the underlying work to it and, therefore, can use it freely. However, it is important to understand that ownership of the NFT does not necessarily entail ownership of the intellectual property (IP) rights attached to the underlying creative work to the NFT. This means that, generally speaking, the buyer of an NFT will probably only have the rights to access / use the underlying work for personal use.
The author of such underlying work is, by default, the owner of all intellectual property rights over the same, including both moral and patrimonial rights (please note that under Spanish intellectual property law, moral rights cannot be waived and are inalienable (i.e. cannot be transferred) as opposed to patrimonial rights which can be freely transmitted).
Therefore, to own the patrimonial rights attached to the underlying work of an NFT, such rights shall be transmitted by the rightful owner to the buyer of the NFT; and such transmission shall be expressly regulated in order to be effective (e.g. by means of an additional contract to the purchase of the NFT regulating the transfer of certain IP rights). At the end, the extent of the IP rights acquired by the purchaser of an NFT will mostly depend on what the author contractually stipulates together with the sale of the NFT.
In line with the above, it is also relevant to take into consideration that the creation of an NFT (or better said, minting NFTs of copyright protected works) requires that the minter / seller of an NFT duly owns the IP rights of the work it represents (or any other relevant rights, such as image rights) in order to avoid possible copyright or other infringements. It is therefore of utmost importance that the author of the work whose rights are being infringed registers their intellectual property rights in the Intellectual Property Register prior to the sale of their work in order to take the legal action they deem appropriate against the person who tokenised their work in an unlawful manner.
(1) In Spain, rights over patents, trademarks and alike are not covered by “intellectual property laws” but industrial property ones.