One of the best Bot-Sentry built-in features, the Captcha. The captcha can be fully configured and customized, while it will still be hosted in our servers, so basically everyone can use this feature, even the worst shared-hosting will have access to this feature without any setup requirement.
By default, Bot-Sentry uses https://notbot.es as a default one, your users will be linked there to join the server during a really strong bot attack.
You can customize the captcha thru https://cyberdevelopment.es/BotSentry/verify/custom, changing texts and colors you can achieve something like this one:
When you customize your website, just click on the Green Button, and it will generate a large link. Then, you can simply make a redirection from your domain to that large link, or use an URL Shortener.