I once had a job in which I was asked to modify the girl with a balloon. I was never given any contact details except for an email address to who I was told was Banksys manager. Considering the extent to which I butchered the artwork for a specific event I was quite shocked at how quickly I was given approval to show the piece that I had modified. I guessed that there probably was no such manager. I also guess a few people do help out with the projects but I think it's one person conceptually behind it all.

Interesting story.

Perhaps Banksy needs to read this:

https://en.wikipedia.org/wiki/Digital_signature

I think part of the point is that Banksy doesn't really care.

His instagram page and website show his works and the latter keeps a running tally of unauthorized exhibitions[1], so I imagine they'd list any fake/unauthorized works if discovered.

[1] http://banksy.co.uk/shows.asp

How do we know the Instagram is run by the original Banksy? Maybe "Banksy" is like the Dread Pirate Roberts, a title held by many people at different times.

I expect the real Banksy would make it known.

I believe klipt's point is that a group of people may agree to use the name (potentially at different times), not that someone is using it without the originator's consent.

There's a site that authenticates pieces for him: https://www.pestcontroloffice.com/whatispco.html although I don't think they'll authenticate the counterfeit Diana notes he made and obviously that wouldn't stop with approval.

Almost every single big graphic artist from the first painters up to current ones has a workshop with sometimes three or four "layers" of management, but plans and controls the vision himself. I suspect Banksy is no exception.

"how do we know that Banksy's art is all by the same person?"

We don't.

"What prevents others to publish art under Banksy's name (with or without approval)?"

Whoever owns or manages Banksy's brand and instagram profile.

Most of the pieces show up on their instagram