After some investigation:
A site visitor to a website that Cloudflare is protecting can see a captcha for the following reasons:
1.The IP address you are on has shown problematic activity online recently in one of our data sources. If you would like to look your IP up, then please look your IP up at Project Honeypot. If the IP address shows data for malicious activity, you can see why there. You can also attempt to whitelist your IP directly on that page by connecting from that IP.
I have searched up your IP addresses and I’ve found the following:
The Project Honey Pot system has detected behaviour from the IP address consistent with that of a mail server and dictionary attacker.
Your IP also appears in multiple spam lists such as spamhaus and spamcop.
If you are innocent of these blacklists then contact your ISP and ask them to provide you with a new IP address, or reset your router if you’ve got a dynamic IP address assignment.