You're not the first one to think of this: https://en.wikipedia.org/wiki/Challenge%E2%80%93response_spam_filtering https://en.wikipedia.org/wiki/Challenge%E2%80

You're not the first one to think of this: https://en.wikipedia.org/wiki/Challenge%E2%80%93response_spam_filtering https://en.wikipedia.org/wiki/Challenge%E2%80%93response_spa...