Owning a non-fungible token rarely means owning a picture stored on a blockchain. In most cases the chain holds a reference, and the file it refers to lives somewhere else entirely.
The token records an identifier and a link
A standard token contract tracks which address owns which token number. That is the whole of the ownership record, and it contains no artwork.
Alongside it sits a function that returns a location for each token's metadata, typically a document describing the name, traits and the address of the image file.
So there are two hops between the chain and the picture: token to metadata, metadata to file. Either hop can break independently of the ownership record, which stays intact regardless.
Web addresses and content addresses behave differently
If the link is an ordinary web address, the file is whatever the server at that address chooses to serve. It can change, move, or stop responding.
Content addressing works the other way around. The identifier is derived from the file's own contents, so a given identifier can only ever resolve to one exact file, and any alteration produces a different identifier.
This is why content-addressed storage is preferred for collections that intend to last. It does not guarantee the file exists somewhere, but it guarantees that what you get back is what was minted.
Availability still depends on someone hosting it
A content address proves identity, not existence. Some machine has to keep a copy and be willing to serve it when asked.
Distributed storage networks handle this by paying or incentivising nodes to retain data, and many projects also pin copies through a service so at least one reliable host is always present.
When a project winds down and stops paying for hosting, the token remains transferable while the image quietly stops loading. Marketplaces then display a blank frame against a perfectly valid ownership record.
Fully on-chain art avoids the problem
A smaller category of collections stores the artwork in the contract itself, either as encoded image data or as code that generates the image when called.
Storage on chain is expensive, so this approach favours compact forms: vector shapes, text, or algorithms that produce output from the token number alone.
The payoff is that the art has exactly the same durability as the ownership record. As long as the chain exists and can be read, the image can be reconstructed with no external dependency.
Mutability is a design choice worth checking
Some contracts allow the owner to change the location that metadata points at, which is useful during a staged reveal and dangerous afterwards.
An updatable pointer means the artwork attached to a token can be replaced by whoever holds the administrative key, without touching the ownership record at all.
Collections that intend permanence usually renounce that ability once the reveal is complete, and whether they have done so is visible on chain for anyone who reads the contract.