It would be good to add a feature similar to fail2ban where if there is a ban the time for the number of posts before a poster makes a new image poster is doubled automatically. It could have a cool down periods when it decreases in half every 10 minutes or X minutes to scale it dynamically down when there are no bans but it automatically scales the effort required to spam.

It would require more work to implement those features though, but you could do something in the database to check the current tally so it's ACID compliant. So, you have worker script checking the ban status and a script reading for the tally from a database table to apply the actions accordingly the board settings.