How do I know an Ordinals collection is authentic?

Check whether its items are children of a single parent inscription. If they are, the collection is defined on chain and anybody can enumerate it. If they are not, you are trusting whoever published the list.

What stops someone copying a collection?

Nothing stops them inscribing the same images. What they cannot do is make those inscriptions children of a parent they do not hold, which is why parent-based provenance is the thing worth checking.

How to verify an Ordinals collection yourself

There is no registry that makes a collection real. What exists is provenance on chain and lists published by marketplaces, and only one of those is something you can check without trusting anybody.

Anybody can inscribe anything, including a pixel-identical copy of somebody else's artwork. Nothing on Bitcoin prevents it and nothing should. So "is this collection real" cannot be answered by looking at the picture.

Two kinds of collection

A published list. Someone maintains a file of inscription ids and marketplaces ingest it. This is how a great many collections work. It is fine, and it means the collection's boundary is whatever that person says it is. Verifying it means trusting them.

Provenance on chain. Every item is a child of one parent inscription. The boundary is not a file — it is a fact about the chain, and anybody can enumerate it from any indexer without asking permission.

Checking a parent-based collection

Take one item and ask what its parent is:

/r/parents/<inscription id>

Then ask the parent for its children, and count:

/r/children/<parent id>/inscriptions/0
/r/children/<parent id>/inscriptions/1
...

Paginated at 100 per page, oldest first, with a more flag. If the total matches the advertised supply, the collection is exactly what it claims and you did not have to trust a soul to find out.

For C.A.T. the parent is be813be7d5ab89e5b7059b28bb4419d09e2988e42bf066ff0987ea555f6439fbi0, and the count is 2,222.

What this does and does not prove

It proves the items were created by whoever held the parent at the time. That is genuinely strong: a copycat can inscribe identical images but cannot make them children of a parent they do not control.

It does not prove the art is original, that the creator is who they say, or that the project will still be interesting next year. Provenance answers "is this one of the real ones", which is a smaller question than "is this good" and the only one a chain can settle.

The other things worth checking

Is the art on chain? Fetch /content/<id> from an indexer. If what comes back is a link to a server or an IPFS hash, the artwork is not on Bitcoin — the pointer is.
Does it render without the project's website? A recursive inscription should assemble from on-chain parts alone.
Do the numbers add up? Supply, inscription range and the block it was inscribed in are all checkable, and all three are easy to overstate in a description.

Questions

How do I know an Ordinals collection is authentic?: Check whether its items are children of a single parent inscription. If they are, the collection is defined on chain and anybody can enumerate it. If they are not, you are trusting whoever published the list.
What stops someone copying a collection?: Nothing stops them inscribing the same images. What they cannot do is make those inscriptions children of a parent they do not hold, which is why parent-based provenance is the thing worth checking.

See the collection this came from