Captchas are used by Poloniex to protect our website, and ensure that bots and bad actors aren’t using our systems. You should see this security precaution in the form of a box entitled “I am not a robot” that prompts you to check a box:
If you are running into captcha issues, please ensure that you are not using an anonymous browsing or an ad-blocking browser extension. Those can interfere directly with the captcha service, so please disable those extensions temporarily or try a different browser and then try again. We also recommend using our mobile applications to login in these cases.
If you continue to encounter issues, please create a ticket through our Support Center and we will be happy to help you troubleshoot the issue. So we can best assist, please be sure to provide screenshots of the issue you are facing.