There seem to be a lot recently. I'm thinking we either,
A: Move to more effective means of screening, such as asking common questions that a computer can't know but a human can figure out (eg, "What color are Pikachu's cheeks?" "What did that guy yell before kicking the other guy into the pit in that Spartan movie?" "What does John Snow know?"), or perhaps a pictographic identification ('select the pictures that contain a dog/flower/ship'), or simply manually OK each account. The last one may be easiest, as we probably won't have many real people flooding in any time soon.