In the CloudFlare Web Application Firewall you are able to block, whitelist, CAPTCHA, or JavaScript Challenge traffic based on IP address, country name, or ASN. The only note provided on the CAPTCHA section is:
If you are unsure whether suspicious web visitor behavior is illegitimate traffic, you can set up a challenge page. This page asks visitors to submit a CAPTCHA successfully to continue their action. If the web visitor fails the challenge, they will be blocked from your website.
What do the CAPTCHA and challenge pages looks like?