Since the insertion of illicit content into public blockchains can have severe consequences for users, we explore and discuss the design space for preventing this insertion.
Our findings show that firewall-like scanning of Bitcoin transactions poses no viable solution to the problem.
However, while content insertion cannot entirely be prevented by technical means, self-verifying blockchain identifiers make currently simple manipulations hard.
Finally, the introduction of mandatory minimum fees can be used to disincentivize content insertion additionally.