Please note that the internal captcha solver is under development.

Currently, the following captchas are supported:

phpBB2.x default captcha
phpBB3.x Simple Image
SMF1.x Very simple - plain text on image
SMF1.x Simple, rotated overlapping letters, no noise
SMF1.x Meduim, rotated overlapping letters with noise
SMF2.x Very simple - plain text on image
SMF2.x Simple, rotated overlapping letters, no noise
ExpressionEngine captcha
ReCaptcha (experimental, not fully implemented!) 

More captchas will be added over time.

You can set the number of retries in the Internal OCR settings window.
Please note that when the OCR fail, it will fallback to whatever you have enabled, manual captcha and/or decaptcher services.