v2 of the Google reCAPTCHA system.
https://developers.google.com/recaptcha/docs/display
Widgets
Get access to data on 5,101,148 websites that are reCAPTCHA v2 Customers. We know of 2,661,141 live websites using reCAPTCHA v2 and an additional 2,440,007 sites that used reCAPTCHA v2 historically and 1,496,215 websites in the United States.
Get a list of 5,101,148 websites using reCAPTCHA v2 which includes location information, hosting data, contact details, 2,661,141 currently live websites and an additional 2,615,674 domains that redirect to sites in this list. 2,440,007 sites that used this technology previously and 1,496,215 websites in the United States currently using reCAPTCHA v2.