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Tutorials
GSA Captcha Breaker Ultimate Tutorial & Honest Review – The All-In-One Automatic Captcha Solving Tool How To Automate Captcha Solving With GSA Captcha Breaker
SDK
Some good tutorials have been written by very active forum user Ozz (thanks again):
SDK for Dummies - How to improve existing captcha definitions
SDK for Dummies - How to make your own captcha definition