pokemon.trade/app/controllers/registrations_controller.rb

class RegistrationsController < Devise::RegistrationsController
  prepend_before_action :check_captcha, only: [:create] # Change this to be any actions you want to protect.

  private

  def check_captcha
    unless verify_recaptcha
      self.resource = resource_class.new sign_up_params
      resource.validate # Look for any other validation errors besides Recaptcha
      set_minimum_password_length
      respond_with resource
    end
  end
end