Basically, twelve members of the collective swapped identities, snagging themselves digitally-altered ID cards that featured blended images of their portrait and another person's. Make Money Not Art explains further: "With the same haircut, twelve members of Ztohoven took a portrait pictures and using the Morphing software they merged every two faces into one. They applied for new IDs with these photos, but each of them used the name of his alter-ego."
Source: ZTOHOVEN
For six months, they then lived under each others' identities, purchasing guns, voting, and even getting married. They documented the entire project, which, in a nod to Kafka's identity-thieved Josef, they called Citizen K.
Sounds like an advertisement for facial recognition audits of ID card applications.
Official web page for "Citizen K." (English)