Banksy's anonymity makes it hard to authenticate his pieces and prints, so Banksy has created a nonprofit called "Pest Control" that issues certificates of authenticity: you send them an alleged Banksy print and £65 and if they agree that it's authentic, they'll return it with a certificate that has a torn-in-half "Di-faced" fake banknote with Lady Diana's face on it, with a handwritten ID number across the bill.

As Clinton Freeman points out, this is a great piece of cryptographic engineering: faking a Banksy cert involves matching the tear precisely, and also requires that a would-be counterfeiter know what was written on the other half of the note, which is stored at Pest Control and is not made available. //

Can an information system be art? Because, like I said, it’s flipping sweet, and all executed in Banksy’s trademark tongue in cheek style. This whole authentication process would easily be my favourite artwork by Banksy.