write your own? many personal tech blogs do this for comment forms and the like. any kind of ambiguity that’s natural for a human to parse accurately but not obvious for a machine is fair game. most bots won’t one-off a solution for smaller sites, so it doesn’t need to be too fancy. for larger ones where one-off customizations might be more likely, lots of engineering resources go toward security and fraud prevention already, so they can afford more sophistication.

but more importantly, in the long term, it needs policy and legal progress. it needs to be costly and international (via treaties/sanctions).