What if we sent the captcha to them by e-mail as a two megabyte image attachment?
Anyone trying to do things with bots would need an e-mail server that can handle tens of thousands of 2 MB e-mails, and ALL e-mail service providers would be able to insta-ban them based on bandwidth usage. Heck we can even make it easy for e-mail service providers to recognize our 2MB capcha e-mail images, by naming them capcha.jpg. Any account that gets more than 10 captcha e-mails in a single day is banned by gmail/yahoo/etc.
I swear, I'm a fucking genius. This only took me 30 seconds to think of.
please give me your email to send you several hundred emails every day. Your 7Gig at google will vanish quite quickly, besides you getting banned for being a spammer... oh wait..