The next update of Grepolis (2.3) will have new bot detection system that uses captcha. All versions of this bot will be detectable.
Although most servers are still at version 2.29 a few have already been updated to version 2.3. Thus be careful and stop using the bot when your server is updated to version 2.3.
If you want to help solve this problem you can help gather information. Things I would like to know are:
-After what actions is the captcha check activated?
-What is the connected timer of the bot when you see the captcha check.