BLOCKCHAIN & WEB3 FUNDAMENTALS - Chapter 8, Exercise 2 Solution
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Correcting "I Own the Image, Permanently Stored on the Blockchain"

PROBLEM
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A friend buys an NFT and says: "I now own this image file, and it's
permanently stored on the blockchain forever." Using this chapter's
own explanation of what ERC-721 actually stores on-chain, correct this
claim.

SOLUTION
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This claim conflates two genuinely different things: the on-chain
ownership record, and the actual image file itself. They aren't the
same, and only one of them is really "on the blockchain."

What an ERC-721 token actually stores on-chain, per this chapter, is:
a unique token ID, the current owner's address, and typically a URI -
essentially a link - pointing to off-chain metadata. That metadata
usually contains a further link to the actual image or media file,
which is normally hosted somewhere else entirely (a regular server, or
a system like IPFS), not embedded directly inside the blockchain
itself.

So your friend does genuinely, verifiably own something real and
permanent: the on-chain ownership record itself - the fact that token
#X is recorded as belonging to their address - is exactly as secure
and tamper-evident as anything else this course has covered (Chapter 3's
own chaining, Chapter 4's own proof-of-work security). That part really
is permanent in the sense this course has established.

What isn't necessarily permanent is the image file the token's own
metadata points to. If the server or storage location hosting that
image ever goes offline permanently, the on-chain record still exists
and still says your friend owns token #X, but the link that record
points to could stop resolving to anything. The blockchain guarantees
the ownership record, not the continued availability of the linked
media.

ANSWER: Your friend genuinely, permanently owns the on-chain token and
its ownership record - that part is accurate and secure. But the image
file itself typically isn't stored on the blockchain at all; it's
usually hosted off-chain and merely linked to from the token's
metadata, meaning the image's own permanence depends on that off-chain
hosting continuing to exist, not on the blockchain itself.

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WHY THIS WORKS AS AN ANSWER

This separates the two distinct things being conflated in the original
claim (the on-chain ownership record vs. the off-chain media file) and
correctly states which one the blockchain actually guarantees
permanence for, using the chapter's own three-part on-chain data
description (token ID, owner, URI) as the basis.