Buying a non-fungible token rarely puts an image on a blockchain. What is recorded is ownership of an identifier and a reference to where the content can be found.
Storage on chain is priced by the byte
Every node stores everything written to a chain permanently, so storage is charged accordingly and the cost is far above ordinary hosting.
An image of any reasonable quality would cost an unreasonable amount to write, and a collection of thousands would be prohibitive.
Collections therefore store a pointer, and the artwork sits on infrastructure priced like ordinary storage rather than like consensus-critical state.
This is not a shortcut taken by careless projects. It is the standard arrangement, and the token standards were written on the assumption that content would live elsewhere.
The token records ownership and a reference
The contract maintains which address owns which identifier, and that record is what transfers when the token is sold.
Alongside it sits a reference to a metadata file listing the name, traits and image location.
Ownership is therefore fully on chain while everything a person actually looks at is resolved by following that reference.
The type of reference determines durability
A pointer to a web address depends on someone continuing to pay for that domain and server. If either lapses, the reference resolves to nothing.
Content-addressed storage instead derives the address from a hash of the file itself, so the reference can only ever resolve to the original content.
That removes the possibility of silent substitution, but it does not guarantee availability, since someone must still keep a copy hosted.
Mutability is the underrated risk
Where metadata sits behind a conventional address, whoever controls it can change what the token points to after it has been sold.
Some collections rely on this deliberately for reveals or upgrades, which means the capability is present by design rather than by oversight.
A buyer inspecting a contract can see whether the reference can be changed and who is permitted to change it, which is a more useful question than where the file is currently hosted.
Fully on-chain collections make a different trade
Some projects generate artwork from code stored in the contract, so the image is produced from chain data with no external dependency.
This constrains the art to what can be generated cheaply and compactly, which is why such collections tend towards generative and vector styles.
What they gain is permanence that matches the ownership record, so the token and the thing it represents share the same lifespan.