ricKAPTCHA

A reCAPTCHA-like UI for rickrolling.

If you are unaware of reCAPTCHA, it's a service provided by Google basically for verifying users are not robots.

If you are unaware of recent changes to reCAPTCHA, see news coverage and various discussions:

• Only approved phones can pass Google’s new reCAPTCHA, locking out privacy-focused alternatives (Lobsters discussion)
• Google Broke reCAPTCHA for De-Googled Android Users (Hacker News discussion)