Starting at block 456476, each banknote represents one block in the chain. The history of that note's block is represented by a hieroglyphic white bar towards the bottom of the banknote, with a timestamp just above it to the right.
What's in the middle of the note is deliberately abstract. Dörfelt's view is that the imagery should reflect the connotations of privacy and anonymity offered by Bitcoin, although the colours within each note are based on the volume of transactions. More colour corresponds to greater volume.
Dörfelt produced the work through his own port of paper.js in Lua, which generates a random seed based on the block identifier hash.